What does M mean in music?

In dynamics, m stands for "mezzo", which means "moderately".

m is used in front of p or f, where p stands for "piano" (soft), and f stands for "forte" (loud). Which means that mp stands for "mezzo piano" (moderately soft), and mf stands for "mezzo forte" (moderately loud).

But there isn't a dynamic called m by itself.

Regards,

AMC