They are playing a duet. When a soloist and a drummer are really "hooked up" or "in sync" (whatever you want to call it, the soloist can signal to the piano and bass to lay out (or if they are REALLY listening they can just hear that it's time to lay out for a chorus or so.) This will allow ht e soloist and the drummer to really speak and interact, unencumbered by keeping strict time or playing the changes. It's a conversation (like Rodge said.)
Allan liked to play duets with drummers, Gary and Chad both told me that this was something that Allan really liked to do. I think on Gary's old instructional tape he and Allan played a duet. And I have seen him do it live with Gary, Chad, and (I think) Novak and even John Marshall as well. Musically it can be very freeing, there is a long history of it in the jazz idiom.
Who else could get away with this? Off the top of my head. Jack DeJohnette and Mike Brecker, Elvin and Coltrane, Roy Haynes and Coltrane, Rashied Ali and Coltrane, Max Roach and Cecil Taylor (or Anthony Braxton,) Tony Williams and Cecil Taylor, Bill Stewart and Joe Lovano, Bill Stewart and John Scofield, Weckl and Oz (I think,) Jeff Watts and Branford, Steve McCall and Fred Anderson, Steve Smith and Mike Stern, Omar and Branford (with Sting, I think?) Peter Erskine and Wayne Shorter, Eric Gravatt and Wayne Shorter, Eric Gravatt and McCoy Tyner... I could go on for days. The first jazz duets that I ever heard were a 1947 recording of drummer Alvin Stoller and trumpeter Roy Eldridge.
It's high level improvisation!!! Think of it this way. Two people are having a conversation while speaking simultaneously. Both people are listening, talking, leaving space, and reacting to what the other person is saying ALL at the SAME time, SIMULTANEOUSLY! This is actually an old acting-improvisation excersise.
It's really cool to hear to actors do it well. And even cooler to hear two GREAT musical improvisers do it with their instruments inside of a musical context. It's very difficult to do, and requires BIG ears and a lot of trust between the two musicians. But it can be wonderful for really freeing you up, both in practice and in performance. And... IT'S FUN !!!!!!!!
Rodge, How many tracks is Vinnie on, on that Rich Ruttenberg record, who else is on it?
Hope all are staying heathy and safe during these VERY strange times!
I love doing duets. First time I heard a duet was Elvin and John and Weck and Chick ( tales of the daring pt3).