- magic square
- magic square for addition and multiplication
- magic sum
- magnetic azimuth
- magnetic declination
- magnetic disk memory
- magnetic meridian
- magnetic meridian plane
- magnetic needle
- magnetic north
- magnetic tape memory
- magnetohydrodynamic turbulence
- magnetosonic wave
- magnitude
- magnitude of a directed line segment
- magnitude relation of cardinal numbers
- Mahalanobis distance
- Mahler measure
- Mahler's classification
- Mahlo cardinals
- main effect
- main memory
- main program
- main rearrangement theorem
- main sequence star