What it is with Far Cry 4 is a deal Sony done with Ubisoft which gives the playstation version of the game 10 keys that you can send to whoever else has a playstation but doesn't have the game.
Each key gives that person 60 minutes to play the game on his own if you let him or team up with you in a Co/op match.
But that expires after 60 minutes and then you are left with 9 keys ,you can continue gifting him another key after the time limit has expired ,again you use another one of your keys.
So in theory myself and you Nelly can gift all our keys to Swanny and he can play the game for 20 hours......But this ain't going to happen

Swanny won't by the game if we dine that and all I'm giving him is 1 hour......

and that's if he behaves....