To expand on Nordicfrost's definintion, Banzai is also notable in that it allows live interactivity with the on screen action(on the E4 channel on Sky Digital in the UK, anyway).
Example question.
Which other Doctor Who do you think that Peter Davidson would have bottom sex with in order to save the Earth from Daleks?
1. Tom Baker
2. Jon Pertwee
3. Sylvester McCoy
An excessively stupid television show, but very entertaining. Currently being repeated on Channel 4, but without the interactive gubbins, unfortunately.
My favourite bet was the 'Can the old lady drink a pint of sherry before fish out of Marillion can start singing Kayleigh' challenge.

BTW, Peter Davidson opted for Sylvester McCoy.