Look up Pokerstars equity cash out and you'll get an explanation, I'm sure it'll be similar. To summarize It's a cash game feature that allows you to cash out your equity when you get all-in (for a fee). So if you get it in with AA vs KK, and choose to cash out you will get 82% of the pot minus whatever the fee is. If the other player doesn't agree and they hit the K you'll get your 82% of the pot while they'll get the whole pot. If you would have won the 18% goes to ACR.
Phil Hellmuth would love this option. lol