- MVTR
- Mach number
- Machinability
- Machine press
- Machine tools
- Machining
- Macrocycles
- Macromolecules
- Macropores
- Macroscopic scale
- Macular degeneration
- Maghemite
- Maglev
- Magma
- Magnalium
- Magnesite
- Magnesium
- Magnesium alloy
- Magnesium bicarbonate
- Magnesium bromide
- Magnesium carbonate
- Magnesium chloride
- Magnesium citrate
- Magnesium deficiency
- Magnesium fluoride
- Magnesium hydride
- Magnesium hydroxide
- Magnesium nitrate
- Magnesium peroxide
- Magnesium phosphate
- Magnesium silicide
- Magnesium stearate
- Magnesium sulfate
- Magnesium sulfite
- Magnetic
- Magnetic bearings
- Magnetic circuit
- Magnetic confinement fusion
- Magnetic cores
- Magnetic dipoles
- Magnetic domains
- Magnetic fields
- Magnetic flux
- Magnetic hysteresis
- Magnetic moment
- Magnetic monopoles
- Magnetic refrigeration
- Magnetic separation
- Magnetite
- Magnetization
- Magnetohydrodynamics
- Magnetometers
- Magnetoreception
- Magnetoresistance
- Magnetorheological fluid
- Magnetosphere
- Magnets
- Magnox
- Magnus effect
- Maillard reaction
- Main lobe
- Main-group elements
- Maintainability
- Malabsorption
- Malachite
- Malaria
- Maleic anhydride
- Maleimide
- Malic acid
- Malignancy
- Malleable iron
- Mandrels
- Manganate
- Manganese
- Manganese dioxide
- Manganese oxide
- Mangroves
- Mantle
- Manual transmission
- Maraging steel
- Marangoni effect
- Marble
- Mariana Trench
- Marine clay
- Marine debris
- Marine heatwaves
- Marine pollution
- Marine snow
- Market share
- Marketing
- Martensite
- Martensitic stainless steel
- Masers
- Masonry
- Masonry veneer
- Mass attenuation coefficient
- Mass diffusivity
- Mass fraction
- Mass number
- Mass production
- Mass spectrometry
- Mass transfer
- Mass-energy equivalence
- Massicot
- MasterFormat
- Material properties
- Material selection
- Materiality
- Materials science
- Mathematical optimization
- Matrix multiplication
- Matter wave
- Mauveine
- Maximum and minimum
- Maximum bubble pressure method
- Maximum energy product
- Maxwell's equations
- Maxwell-Boltzmann distribution
- Mean curvature
- Mean free path
- Measurement uncertainty
- Mechanical advantage
- Mechanical energy
- Mechanical engineering
- Mechanical equivalent of heat
- Mechanical load
- Mechanical properties of biomaterials
- Mechanical testing
- Mechanical wave
- Mechanically stabilized earth
- Mechanism of action
- Media filter
- Median
- Median lethal dose
- Medical devices
- Medical diagnosis
- Medical gloves
- Medical imaging
- Medical ultrasound
- Medications
- Medicine
- Medieval Warm Period
- Mediterranean Sea
- Medium wave
- Mega
- Melanin
- Melanocytes
- Melting
- Melting point
- Membrane potential