Improvisation

From Conservapedia

Improvisation ("improv") is a when a performer is "making it up he/she goes along".

In music, improvisation is when one sings or plays music which is made up on the spot; it is neither memorized nor written down. Improvisation is often found in jazz, blues and rock and roll.

Actors also sometimes improvise. Some comedy troupes base their entire act on improvising.