A free spins bonus is a special casino offer on slot machines to get acquainted with the corresponding slot machine and casino. Usually you can only play specially selected new slots games. The offer differs a bit depending on the casino, but the principle is always the same; play for free, and the winnings are then converted into a bonus, which has to be unlocked through a wager; the number of times you will have to play with the money you have won, before you can withdraw the funds. Such a wager is usually between 20x and 30x.