Slots bonuses normally have a lower playthrough than blackjack bonuses. The playthrough is the amount you must wager (make in total bets in your time playing on that deposit) before cashing out from the casino. For example…
someone wants to take a 100% match welcome bonus with 20 x playthrough. They deposit $25, so the casino matches that with 100% which is $25. So the player has $50. The playthrough on this bonus is 20x. So the player must make in bets $50 x 20 before withdrawing from the casino. This means the player must make $1000 of bets before they withdraw. For example, spin a slots game 1000 times (win or lose) before cashing out.
Hope this helps when choosing.