Abscissa
The 
- (horizontal) coordinate of a point in a two dimensional coordinate system. Physicists and astronomers sometimesuse the term to refer to the axis itself instead of the distance along it.
- Morgado Identity
- Morgan-Voyce Polynomial
- Morley Centers
- Morley's Formula
- Morley's Theorem
- Morley's Triangle
- Morphism
- Morrie's Law
- Morse Inequalities
- Morse Theory
- Morse-Thue Sequence
- Mortal
- Mortality Problem
- Morton-Franks-Williams Inequality
- Mosaic
- Moser
- Moser's Circle Problem
- Moss's Egg
- Motzkin Number
- Moufang Plane
- Mousetrap
- Mouth
- Moving Average
- Moving Ladder Constant
- Moving Sofa Constant