Placing a fist into the rectum or vagina, hopefully with lots of lube, practice and relaxation on the part of the receiver. It can be a male fist or a female fist, but if you hold the average male hand against the average female hand, some people might prefer the woman’s hand. The term is a misnomer, since the hand goes in with the fingers extended and fingertips bunched together rather than in a fist. However, once it’s inside, all bets are off.