What is another word for improvisational performance?

Question

Again, I can't recall the word.

It was a short word, and it's something related to an improvisational and small concert (performance)in a bar.

I know there's a word but I can't even recall its exact meaning, perhaps something related to jazz, like a combo.. and it may starts with letter B.

I'm so sorry for being ambiguous, but really hope someone would like to help me with the word

Answer 1

A jam session is an event where musicians (amateur or professional) get together and play improvised music. There is usually little or no preparation, predetermined plan or set list.