In music what is it called when you pluck a string?

"String piano" is a term that describes unconventional extended pianistic techniques that involves using the strings in other ways than hitting one of the piano's keys.

Plucking the piano's strings (with a plectrum for example, I don't recommend using your fingers directly) is one such technique and it's use is not often seen except in modern art music and film scores. If you are to explain this technique you could either just say "pluck the strings" or "pizzicato" (this term is used on other instruments as well, such as the violin, so it could cause confusion if you are not specific that you are talking about the piano).

Since a lot of pianists may not come in touch with extended piano techniques, they can be skeptic if you want to give thim a score to play which involves plucking the strings. Others think it's just fun to use the piano in this unexpected way.