Pre-level boosters are Choco Boosters; however, the difference is that those are not created by matching candies on a level! You will notice a pre-level menu right before starting a level to play. There, you will see a level of objectives, and the amount of pre-level boosters right underneath! 

You can tap on a pre-level booster you’d like to use, and it will be available among candies as soon as you start a level. Pre-level boosters can be earned from chests or purchased with gold coins. 

You may also notice there are unlimited pre-level boosters. If you earn such a reward, you can use such a pre-level booster on any level for as long as this buff is active. The remaining time until it expires is displayed in a menu before starting a level on a correlating pre-level booster.