This is also sometimes called "all-in insurance" and basically mean, that someone else (in this case the house) takes over the risk / variance. In the classic TV-poker show "Big Game" Phil Helmuth occationally purchased all-in insurance from some of the other players. Most online poker sites have this feature in their cash games now, and usually the fee is 1%.
Example: You have QQ, the opponent have AKo, and you are all-in before the flop. Your chance of winning is 55%, and the pot size after rake is 20$. This mean, your equity share is 11$. If you use the all-in cash-out option AKA "insurance" you will be rewarded 11,00-0,11=10,89$ from the pot. If your opponent also opt to cash out, they will be rewarded 9,00-0,09=8,91$, and PokerStars thus earn an extra 0,20$ in rake. Alternatively if your opponent dont cash out, the board will be run out, and he will then either be rewarded the full 20$ pot or nothing with him now essentially gambling with the house like in casino games.