See Clans for details; the two terms are synonyms. But nobody calls them Guilds in Season Two! 1)2)3)4)5)

1)
Nobody called them Guilds in Season One, either. Or in the Pilot. Unless they'd forgotten which game they were playing.
2)
Uh-huh.
3)
Seriously, it's always been Clans!
4)
Mmhm. And the Pleasantville train station has always been right in town.
5)
Okay, so it's the Wiki of Lies. They've still never, ever been called Guilds.