Minus six is a card game that has a rule called "exile".
Think of "exile" as when you go to time out. When you break a rule in the card game, you get sent to the "exile" zone.
When you go to the "exile" zone, it means you are out of the game for a little while. You can't use that card or do anything with it until the game is over. It's like being in a time out corner.
But, just like when your time out is over, you can come back and play again. When the game is over, you can use that card again in the next round.
That's what exile means in minus six. It's just a rule to make sure everyone plays fair and follows the rules.