Immortal: The best hand that can be made.

Improve: To make a better hand by hitting cards during the betting rounds.

In the hole: A card dealt face down. Also refers to by how much you are losing a game.

In The Money: To make it far enough in a tournament to place in the money.

Inside Straight: Making a straight by catching the middle card.  Also called a gut shot straight.

Isolate: To make a raise that will deter other players to stay in the hand.  Usually you want to isolate to play against one other opponent.