Fap is a slang term for male masturbation. The term alludes to the sound a man’s testicles make slapping against the body or against the hand when he pleasures himself. The earliest known use of the word fap appeared in the Japanese manga webcomic Sexy Losers in April 1999. The term has since spread to common mainstream use, particularly online.
Fap is the male equivalent of the similarly onomatopoeic terms for female masturbation, schlick, paff, and squish.
More About Fap
The term fap can be used in many ways. It can be used as a noun, as in the sentence “I think my parents heard me having a fap last night.” Fap can also be used as a verb, as in the sentence “I think I’ll stay home and fap tonight.”
Fap can also be used to suggest someone is so attractive that they would inspire you to masturbate, especially online. In this usage, someone might write “Did you see the picture X posted online last night? *fap fap fap*” This sentence indicates person X is sexually attractive. Someone might also reply simply “Fap fap fap” in response to a suggestive image or comment posted online. This sentence indicates the commentor will think about what was posted later while masturbating.
The term implies a kind of rough and aggressive male masturbation since the more furiously a man masturbates, the more likely his body is to make the fapping sound.