Rakeback is one of the most important promotions that some poker rooms offer to its players. This offer consists in returning a % of the commission that the players pay on each hand when they bet money on the table.
Poker tables tend to take between 3% to 5% of what players bet on the table, and if you join a poker room that offers rakeback, the same room will give you back a % (generally 30%) of what you have paid in commission when playing.