Pink Floyd was an influential British progressive rock group. They are best known for their bestselling albums "Dark Side Of The Moon" (1973), "Wish You Were Here" (1975) and "The Wall" (1979).
Zappa's jam with Pink Floyd in Amougies
Zappa and Pink Floyd performed "Interstellar Overdrive" (an instrumental from Pink Floyd's debut album The Piper at the Gates of Dawn, 1969 ) together during the Actuel Festival (1969) in Amougies, Belgium. However, when interviewed about the matter in They're Doing the Interview of the Century, Part 2, Zappa denied this or simply couldn't remember it. For decades fans weren't sure whether Zappa's jam with Pink Floyd was an urban legend or not? Photos and audio recordings eventually turned up, but it took until 2015  before video footage (and undeniable proof) of this legendary jam finally surfaced. 
On April 2, 1980, Zappa played Pink Floyd's "Another Brick In The Wall, Part 2", when he was a guest deejay on radio station KSJO, San Jose.
Quote about Zappa by Pink Floyd
"Frank Zappa is really one of those rare musicians that can play with us. The little he did in Amougies was terribly correct. But he’s the exception. Our music and the way we behave on stage, makes it very hard to improvise with us." - Pink Floyd member Nick Mason, 1973.