M is the thirteenth letter of the English Alphabet, and a labial articulation, formed by a compression of the lips. It is called a semi-vowel, as the articulation or compression of the lips is accompanied with a humming sound through the nose, which constitutes a difference between this letter and b. Its sound is uniform; as in man, time, rim.

M is a numeral letter, and among the ancients stood for a thousand; a use which is retained by the moderns. With a dash or stroke over it, it stands for a thousand times a thousand, or a million.

As an abbreviation, M stands for Marcus, Martius, Manlius or Mutius.