This refers to a sexual practice in which one person shoves a fist up another person's anus. People who are interested in sado-masochistic sex sometimes do this to each other in their efforts to achieve sexual satisfaction. As the practice would be viewed as dangerous or degrading by many, it is unusual and likely to be considered disgusting by those who don't like painful sex.
Fisting is a sexual activity that involves inserting a hand into the vagina or rectum. Once insertion is complete, the fingers either naturally clench into a fist or remain straight. ... en.wikipedia.org/wiki/Fisting
The sexual practice of inserting one or both hands into the vagina or rectum of one's sexual partner en.wiktionary.org/wiki/fisting
fisted - Having some specific type of fist en.wiktionary.org/wiki/fisted
Slang term - To insert the fist into the rectum or vagina of another as a means of sexual stimulation.12 www.lunco.cfsh.info/sexual-reproductive-health-glossary/glossary-E-F.html
Slang term for a sexual variation in which an individual inserts his or her entire hand into their partner's vagina or anus. www.4sexual-pleasure.com/definitions.html
The practice of inserting the entire hand into the vagina or (less commonly) into the anus. Commentary: Vaginal fisting is actually quite a bit easier to do than most people realize; the human body is quite accommodating. ... www.bdsmgifts.com/bdsm-dictionary/
Hand position with ringers flexed in a clenched palm. This is the normal posture for the first 3 months of life, after which the hand begins to be open or unfisted most of the time. Persistence of fisting past this time is often a sign of hypertonicity (increased muscle tone) or spasticity. www.childrenwithchallenges.info/definitions/F.html