It's for people that don't want to wait for the auction to be over. also sometimes the seller will add more things if GIN is used. Like mine... If you bid normally you get 1 card, if you use GIN you get 20.
It's stand for Get it now. for this auction the winner is going to get 20 cards either way, cuz it's not very fair for the winner to only get 1 card. but if it goes up to 4000 it'll be 25 cards 5000 30 cards.