In sticky bonus, your whole balance is locked to bonus wagering, and you can only cash out any possible winnings after you have fully completed the wagering requirements.
In the non-sticky bonus, you play first with your initial deposit balance, and the wagering requirement only comes into effect when you start playing with the bonus money.
For example, you deposit $100 with a 100% deposit bonus and start playing with a $200 balance. The first $100 is so-called raw money, which you can withdraw in the event of a possible profit. However, if you lose your initial deposit and start playing with the bonus money (the latter $100), the bonus wagering requirement comes into effect and you cannot withdraw your winnings until you have played through the wagering requirement. So the non-sticky bonus is like a second chance if you lose your original deposit.