I have read the following sentence in an Italian learning tool:
Suoneremo quattro o cinque pezzi.
It is clear to me that "pezzo" here means "musical composition" (part of meaning 3b in http://www.treccani.it/vocabolario/pezzo/ ). I think that word with that meaning is usually used only in the scope of opera, musical shows and orchestra. It also seems to me that it is a bit formal and usually it would not be used in an informal talk amoung young friends, e.g., about pop music (e.g., "Adoro il nuovo pezzo di Shakira"). Is that true?