A non-sticky bonus is a casino bonus you can cash out as soon as you've met the wagering requirements. Unlike a sticky bonus, which can't be withdrawn at all.
These days, non-sticky bonuses are far more common than sticky bonuses, which makes non-sticky bonuses the "traditional" bonus. The best way to recognize a sticky bonus is to read the bonus T&Cs of the offer, and see if the bonus is meant only for wagering.
Most players consider a non-sticky bonus easier to understand and handle, making it also a bit friendlier bonus for non-experienced players.