M

M or m may refer to:
* m(n) map, which is used to define Fish number 5
* m(m,n) map, which is used to define Fish number 6
* The margin function m(x) and m1(x), defined with fusible numbers
* The Roman numeral for the number thousand
* The SI prefix mega- for million
* A shorthand for Moser
* Mahlo cardinal
* The symbol for the SI prefix milli-
* Mersenne numbers
* Mathieu groups, see 7,920, 95,040, 443,520, 10,200,960 and 244,823,040
* Monster group
* Hyper-Moser notation
* Middle-growing hierarchy