Jam - extended musical improvisation over rhythmic grooves and chord patterns (the key word here is improvisation, which distinguishes these solos from those which are rehearsed).
Jam Band - an organized musical group with regular members whose live performances and albums are known for extended jams. The most recognized “Jam Band” in history is probably [...]
Another teaser to convince you that you’ve just gotta visit… I’ve created a page with a little sample of what the Blues Jam sounds like. Crank it up really loud and enjoy.