[Jixby Phillips]

Seinfeld has never done any kind of cross-over ON seinfeld. Seinfeld has crossed over onto other shows, like Kramer showing up on Mad About You, but they've never had Pheobe from Friends show up at Monks or anything like that.

Some of you are missing the point, a spin-off or a crossover doesn't nessessarily equal what Gadzooks is talking about. He's talking about some kind of story or character or whatever that starts off in one episode of a show and then ends up being resolved on another show, typically one that directly follows the first show