The Bubble Bowl is large bowl shaped building where Squidward had to perform in front of a live human audience, in the episode "Band Geeks." He has been challenged by his nemesis, Squilliam, and is nervous because his band has not shown to be very good in practice. One night before the big concert, a riot starts up among the band members and Squidward storms off disappointed.
SpongeBob comes to the rescue with an inspirational speech and they practice throughout the night. The next day the band is ready and Squidward Tentacles is nervous. They end up doing amazing and Squilliam fainted with all the singing that he had to be taken to the hospital.
The Bubble Bowl is a parody of "The Super Bowl," since they perform in the middle of an American football field.
It was never seen or mentioned in any other episode.