My friend's child's father is wanting to "sign away his parental rights." What exactly does this mean?

My friend had an “oops” baby. She was messing around with a co-worker and got pregnant, and then he went and remarried his ex-wife. Crazy, I know. Well, now he wants to “sign away his parental rights.” What exactly does this mean? Would he still have to pay child support, or is he off free? She has a lawyer and they’re going to court soon. I just would like to know this for my knowledge. Thanks!