The absolute or relative size, extent or importance of something.
An order of magnitude.
A number, assigned to something, such that it may be compared to others numerically
Of a vector, the norm, most commonly, the two-norm.
A logarithmic scale of brightness defined so that a difference of 5 magnitudes is a factor of 100.
A measure of the energy released by an earthquake (e.g. on the Richter scale).