- (countable) An order of magnitude.
- (astronomy) The apparent brightness of a star (on a negative, logarithmic scale); apparent magnitude
- (uncountable, countable) The absolute or relative size, extent or importance of something.
- (mathematics) Of a vector, the norm, most commonly, the two-norm.
- (mathematics) A number, assigned to something, such that it may be compared to others numerically
- (seismology) A measure of the energy released by an earthquake (e.g. on the Richter scale).