A banana seat is a bicycle seat that's vaguely shaped like a banana. Unlike a regular bicycle seat, a banana seat is supported both by a center post and auxilliary posts at the back, which were bent over to form a handle that could be grabbed and held, thereby stopping the bike and causing the rider to crash forward into the handle bars (see Newton's Laws.) Of course that's just a theory since I would never do anything like that. For some reason, I remember banana seats being on girl's bikes rather than being on the boy's.