What is the meaning of Mp?

mezzo piano (quite soft)

Initialism of market price – written on menus instead of a price to mean the price charged depends on the price of supplies, which may vary.

A letter of the Adzera alphabet, written in the Latin script.

Abbreviation of másodperc (second[s]).

Abbreviation of mīlle passūs (Roman mile).

A letter of the Lingala alphabet, written in the Latin script.

Green Party; Abbreviation of Miljöpartiet.

Source: wiktionary.org