Where did the term SnG come from?

[AA suited]

who came up with the term sit and go?

and why is it used for tournys?

[Kurn, son of Mogh]

I don't know who coined the phrase, but it's simply shorthand for indicating that the tournament has no specific starting time; it goes when a prearranged number of players sit.

[codewarrior]

IINM, it was coined by UB.

[MWC]

Interestingly, this is the same policy the Chicago White Sox use for baseball games (10 fans seated? time to play) /images/graemlins/grin.gif