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