Meals and incidental expenses, the food-and-tips portion of per diem, often paid at a partial rate on travel daysIn: Hours, overtime, and per diem proof
M&O
Management and operations, the Uptime Institute assessment of the operations programIn: Data center MOP SOP EOP
m2, m3
Drainage coefficients applied to the unbound base and subbase, adjusting for how well they drainIn: Asphalt pavement thickness design
Black iron-oxide sludge from corroding steel; abrasive to the pump and insulating on coils, and the thing a magnetic separator targetsIn: Hydronic water and glycol field guide
MAHC
The CDC Model Aquatic Health Code, a model code many jurisdictions adopt or adapt for commercial pool depth, markings, slopes, drains, decks, and operation.In: Commercial pool construction
Main / exit cleanout
The cleanout serving the building drain to sewer junction, the access to the whole mainIn: Plumbing cleanout field guide
The single neutral-to-ground bond at the service, where a non-separately-derived generator's neutral stays bondedIn: Generator grounding and bonding
Main drain entrapment
Suction holding a swimmer, hair, or clothing against a drain hard enough to trap or drown; the system's deadliest hazardIn: Pool and spa mechanical systems
Main tee / cross tee / wall angle
The load-carrying main runner, the cross member that forms the tile module, and the L-shaped perimeter trim and supportIn: Suspended acoustical ceiling field guide
Main vs circulation relief valve
The main relief is a large safety valve for over-pressure; the circulation relief bleeds a small flow to cool the pump at no-flowIn: Fire pump acceptance test
Mainline vs lateral
Mainline stays under constant pressure to the valves; laterals carry one zone to its heads when it runsIn: Sprinkler system design
Clearing what an activity needs, such as an RFI, submittal, material, or prior trade, before it is dueIn: Project scheduling
Make-ready / planning
Confirming a task has its materials, tools, equipment, information, approvals, and access in place before the crew starts itIn: Field leadership and the foreman role
Replacing the air the hood exhausts so the building does not go negative, with the kitchen held slightly negative to the dining roomIn: Kitchen equipment install field guide
Maltenes
The lighter, oily fractions of asphalt binder that keep it soft and ductile, lost to oxidation as the pavement agesIn: Fog seal and rejuvenator preservation
Management reserve
Money held above the estimate baseline for unknown-unknowns, the unforeseeable, usually controlled by the owner or senior management rather than the estimator.In: Contingency and risk pricing
The supply and return assembly where all loops in a zone connect, carrying flow meters and actuatorsIn: Radiant floor heating design
Manifold / probes
The gauge set or wireless clamp-on probes that read suction and liquid pressure and temperatureIn: Refrigerant charging field guide
Manifold gauge set
The gauges, hoses, and valves that read refrigerant high and low pressure and connect the system to pump, recovery, and cylinderIn: HVAC test instruments field guide
Manifold pressure
The gas pressure the valve delivers to the burners, set to the data plateIn: Gas furnace field guide
ACCA's residential and light-commercial duct design procedure, built on available static pressure and the friction rateIn: Manual D duct design field guide
Manufacturer warranty
The product maker's coverage of the equipment or material itself, usually longer than the workmanship warrantyIn: Closeout and warranty management
Map pack / local pack
The three-business block of local results above the regular search listings, where review volume, recency, and rating heavily influence who appearsIn: Customer communication and reviews
The estimated job margin eroding toward the actual as costs run over; the WIP shows it earlyIn: Construction cash flow and WIP
Marine-grade fastener
Hardware rated for immersion, 316 stainless in salt water or hot-dip galvanized for fresh, matched to avoid galvanic attackIn: Boat dock and marina construction
Marked volume
The cubic-inch capacity stamped on a body, required before any splice, tap, or device is allowed in itIn: Conduit bodies and fittings
Marked-up set
Any field set in progress, the live working red-line before it becomes the formal as-builtIn: As-built record drawings
Units laid in mortar; CMU is the concrete masonry unit, the concrete blockIn: Masonry construction
Mass concrete
Any placement large enough that hydration heat must be managed to control cracking, often a least dimension of about 3 to 4 ftIn: Mass concrete thermal control
Mass notification / ECS
Emergency communication system: intelligible emergency voice and visible messaging to occupants, life-safety equipment under NFPA 72In: Intercom and paging design field guide
Planting one variety in solid blocks or drifts so the color reads from a distance, rather than dotting single plantsIn: Seasonal color and annual rotation
Mast-climbing work platform (MCWP)
A powered deck that climbs a mast bolted to the building on a rack-and-pinion drive; the whole installation, the platform, mast, ties, and baseIn: Mast-climbing work platform safety
The matrix is the binder and background color; the aggregate is the decorative chip, marble, glass, granite, or recycled glassIn: Terrazzo flooring install and polish
Main, horizontal, and equipment distribution areas, the TIA-942 spaces from the central cross-connect out to the rackIn: Data center structured cabling
A loss-of-productivity method comparing the rate in an unimpacted period against an impacted period of similar work, the gap being the lossIn: Construction labor productivity tracking
Minimum extinguishing concentration, the percentage that just puts the fire out, and minimum design concentration after the safety factorIn: Clean agent room integrity
Mechanical seal
Two lapped faces, one rotating and one fixed, sealing the shaft with a thin water film; it must not run dryIn: Hydronic pump install field guide
A device that joins two reinforcing bars end to end and transfers force bar to bar, not through concrete bondIn: Mechanical splices and couplers
Mechanical vs ventilation dehumidification
Mechanical uses a refrigeration coil to condense moisture out; ventilation brings in drier outdoor air and exhausts the moist airIn: Natatorium HVAC field guide
Mechanically attached
Racking bolted to the structure through flashed penetrations; lighter load, more holesIn: Solar-ready roof provisions
Baseline and periodic exams, including chest X-ray and spirometry, offered to workers who must wear a respirator 30 or more days a yearIn: Silica exposure control program
Medium temp / low temp
Medium temp is a cooler holding product above freezing, commonly in the mid-30s°F; low temp is a freezer holding product frozen, commonly near 0°F to about -10°FIn: Commercial refrigeration field guide
Medium voltage
Distribution voltages roughly 5 to 35 kV, between low voltage and high voltage; sometimes given as 2.4 to 35 kVIn: MV termination and splicing
Meet-me room (MMR) / cross-connect
The MMR is where carriers and tenants interconnect; a cross-connect is the physical cable linking two endpoints through itIn: Colocation fit-out field guide
Micro-electro-mechanical systems; here, an array of tiny tilting mirrors that steer the optical beam inside an OCSIn: Optical circuit switch and photonics
MEP
Mechanical, electrical, and plumbing, the systems that carry most of a data center's cost and scheduleIn: Data center buildout phases
MEP make-safe / LOTO
Capping, disconnecting, locking out, and verifying dead the mechanical, electrical, and plumbing before cutting; LOTO is lockout-tagout of hazardous energy.In: Interior demolition strip-out
Mesh bonding network in the equipment room, commonly 1/0 to the busbar and 6 AWG to each rackIn: Data center grounding and SRG
Metadata / EXIF
The data stored with an image, including timestamp, GPS location, and device, plus any tags or description added at captureIn: Field photo documentation
Metal roof restoration
Renewing an aging metal roof in place by treating rust, repairing fasteners and seams, and coating it, instead of a tear-offIn: Metal roof restoration
Metal-bond vs resin-bond diamond
Metal bonds cut and expose the slab, resin bonds polish it to gloss, with a transitional step betweenIn: Polished concrete grind and densify
Metal-clad
Medium-voltage switchgear with each compartment isolated by grounded metal barriers, per IEEE C37.20.2In: Distribution equipment guide
Metal-clad switchgear
MV switchgear with drawout breakers and fully barriered compartments for the breaker, bus, and terminationsIn: MV switchgear maintenance and testing
Meter setter / horn
The rigid bracket or yoke that holds the meter to its lay length and carries the valves, so a meter can be changed without cutting pipeIn: Water service and meter tap guide
Metered bills the kWh you actually use; committed bills a flat charge for the reserved breaker capacityIn: Colocation fit-out field guide
Metering device
The restriction between the high-pressure liquid line and the low-pressure evaporator that drops pressure and meters liquid into the coilIn: Metering devices field guide
Method A / B / C
The three TIA-568 channel schemes: straight trunk with a flipped cord, reversed trunk, or pair-flipped trunkIn: MPO/MTP polarity methods
MEWP
Mobile elevating work platform, the ANSI A92 term covering boom, scissor, and vertical mast machinesIn: Aerial lift and MEWP safety
Microbiologically influenced corrosion, localized pitting driven by bacteria in residual water, a common dry-system failureIn: Dry-pipe and pre-action trip test
Micro data center
A small, self-contained unit, from a single rack to a few cabinets, with integrated cooling, power, monitoring, and securityIn: Edge and micro data center deployment
Micro fiber
Fine fiber under about 0.3 mm that controls plastic-shrinkage cracking and gets no structural creditIn: Fiber-reinforced concrete
A cold mix using a polymer-modified emulsion that sets chemically, reopens to traffic in about an hour, can be placed thicker, and can fill rutsIn: Slurry seal and micro-surfacing
Microbubble air separator
A coalescing device, best placed at the hot, low-pressure heat-source outlet, that merges tiny bubbles so they rise and ventIn: Hydronic water and glycol field guide
Microbubble separator
An air separator with a coalescing medium that merges tiny microbubbles into bubbles large enough to rise and ventIn: Expansion tank and air field guide
Microburst
A traffic spike that saturates a link or overflows a buffer for well under a second, invisible to slow polling but enough to drop packetsIn: Network observability for the AI fabric
Microclimate
A small pocket where sun, wind, moisture, or temperature differs from the rest of the site, shifting the effective zoneIn: Landscape design and plant selection
Microgrid
A local power system of sources, storage, and load that can island or run grid-parallel under one controllerIn: Data center on-site generation
Federal law requiring performance and payment bonds on federal construction over a dollar threshold; states have Little Miller ActsIn: Surety bonds and bonding capacity
Min / max airflow
The throttled floor and the design ceiling the box modulates between; min carries the ventilation requirementIn: VAV box commissioning field guide
Mineral filler
Portland cement or hydrated lime added to the mix to add cohesion and react with water to drive the breakIn: Slurry seal and micro-surfacing
Minimum airflow
The throttled-down floor, set to meet ventilation without overcooling, bounded by 62.1 and 90.1In: VAV box commissioning field guide
The lowest airflow a box will deliver, set for ventilation per ASHRAE 62.1 and the reheat floorIn: VAV vs CAV air distribution
Minutes
The official record of a meeting: decisions, attendees, action items, and open items, issued and allowed to stand correctedIn: Progress meetings field guide
Miscibility
How well the oil mixes with the refrigerant; poor miscibility means the oil drops out and staysIn: Oil return field guide
Mitigation is the emergency work that stops the loss from worsening; restoration is the rebuild of what was removedIn: Water damage restoration field guide
Mitigation duty
The policy obligation, from ISO-form sue-and-labor language, to take reasonable steps to protect property from further loss after a covered eventIn: Emergency board-up and tarping
Mix design
The approved proportions of cement, water, aggregate, and admixtures to meet specified strength, durability, and workabilityIn: Mix design and water-cement ratio
The lowest F-number allowed in any single test section, so an average cannot hide a local failureIn: Floor flatness and levelness
MMR
Meet-me room, the neutral space where carriers and tenants interconnect through cross-connects, often split into MMR-A and MMR-B for redundancyIn: Cross-connect patch records
Mobilization and demobilization, the trip to start the job and the trip home, and the travel pay that covers themIn: Hours, overtime, and per diem proof
A full-size test wall proven for air, water, and structural load before the building, then confirmed on the installed wall by an ASTM E1105 water test.In: Curtain wall and glazing
Mod-bit
Modified bitumen, an asphalt sheet membrane reinforced with mat and modified with SBS or APP polymerIn: Modified bitumen installation
Modal dispersion
Pulse spreading from many modes arriving at different times, the limit on multimode distanceIn: Data center fiber types
Modbus
A register-based protocol common on chillers, meters, and UPS; no built-in object model, so scaling and register maps must be verifiedIn: BMS and DDC controls commissioning
Modbus / BACnet / IEC 61850
The common protocols meters and relays use to report to the EPMS serverIn: EPMS and power metering
Mode of action / RAC group
How a product kills, grouped by IRAC, FRAC, or HRAC number on the label, the basis for rotationIn: Landscape IPM field guide
Mode-field diameter (MFD)
Width of the light-carrying region in singlemode; a mismatch causes built-in splice lossIn: Fiber splice loss budget
Model + control dependency
The rule that a robot is only as accurate and correct as the coordinated model and the survey control it builds from; a bad model or control yields bad outputIn: Construction robotics
Model-to-field
Exporting coordinated points from the BIM model to the instrument so the field builds exactly to the model on the project coordinate systemIn: Construction layout
Modified bitumen
Polymer-modified asphalt low-slope sheet, applied by torch, mop, cold adhesive, or self-adheredIn: Roofing system types
Modular uses pre-grown cassettes or trays of media on a frame; felt uses geotextile pockets fed hydroponically with no soilIn: Living wall and green wall systems
Modular / self-contained / remote
Head on a separate bin or dispenser; maker and bin in one undercounter cabinet; head inside with the condenser mounted outsideIn: Commercial ice machine field guide
Slab moisture measured by ASTM F1869 emission rate or ASTM F2170 in-situ relative humidity before a bonded pourIn: Terrazzo flooring install and polish
Mold remediation
Controlled removal of mold growth plus correction of the moisture source that fed itIn: Mold remediation field guide
A joint built to open, close, and shear, sealed with a centerbulb waterstopIn: Waterstop field guide
Movement class
The plus-or-minus percentage of joint width a sealant can take, per ASTM C920, such as class 25In: Joint sealant replacement
Movement joint (EJ171)
A soft, sealant-filled joint at the perimeter, in the field, over slab joints, and at changes of plane that lets the tile and building move without tenting.In: Ceramic and porcelain tile installation
Movement range
The total movement the joint must absorb, from thermal swing, moisture, settlement, creep, and seismic drift combinedIn: Building movement joint systems
Movement rating
How far a cover can let the joint open, close, and on a seismic joint shear, before the bellows is overworkedIn: Roof expansion joint installation
Musculoskeletal disorder, injury to muscles, nerves, tendons, joints, or discs, often from overexertion or repetitionIn: Material handling and lifting ergonomics
The mill certificate proving the pipe or component is the alloy and grade the spec requiredIn: Industrial process piping
MTTD / MTTR
Mean time to detect a fault; mean time to restore, repair, or resolve, which are different measures, so state which one you meanIn: Incident management and outage response
MTV (material transfer vehicle)
Machine between truck and paver that re-blends gradation and temperature before the paverIn: Asphalt segregation
The temperature rise each loaded conductor causes in its neighbors, which lowers the ampacity of every conductor in the bankIn: Concrete-encased duct bank field guide
Moisture vapor emission rate (ASTM F1869, lb/1000 sf/24 hr) and internal relative humidity (ASTM F2170, percent), the moisture tests before a coatingIn: Concrete sealers and coatings
MVR
Motor-vehicle record, the state DMV driving history showing license status, violations, convictions, suspensions, and crashesIn: Fleet and driver safety program