M can usually represent the following meanings in mathematics:
1) stands for length unit: meter. This is the abbreviation of British rice (or rice).
2) Representative time unit: minutes. This is the abbreviation of English Minute.
3) stands for one thousandth: milli. This is the abbreviation of English milli, which is usually added before the unit, and the value is one thousandth of the current unit. For example, mg: mg; mm:mm； Millisecond: Millisecond.
4) represent constants, especially integer constants, such as a, b, c, k, n.
unit of length
The unit of length refers to the basic unit for measuring spatial distance, which is formulated by human beings to standardize the length.
Its international unit is "meter" (symbol "m"), and commonly used units are millimeter (mm), centimeter (cm), decimeter (dm), kilometer (km), meter (m), micron (micron) and nanometer (nm). Length units play an important role in various fields.