Connected with Anthropomorphology, yiffed is the past participle of yiff. (That means that it is the past tense of yiff) When two or more anthros have mated, you say, they have yiffed

Yiff, Yiffing, Yiffed. In that order
When we finally got home we yiffed all night.
by Player May 6, 2005
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Yiffing is a combination of words "sniff" and "yell" made up by MatPat's wife Steph in their livesteam for a game Dayshift at Freddy's, as she didn't know what it actually meant.
MatPat: "So, yiffing is, for those who don't know-"
Steph: "Wait, I should guess! I think that a yiff is probably a yell and a sniff at the same time."
by JJTrue October 30, 2016
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Usually refers to cyber sex between two or more members of the furry fandom. Originally refers to the sound that foxes make when mating. Members of the furry fandom may use the term to refer to actual sexual contact, usually in a lighthearted manner.

It is also a term used at furcons to inquire about sexual intentions between fursuiters.
The anthro fox smiled at the mass of horny furres, knowing that a good yiffing session would soon follow.
by Suirel Whitedragon January 28, 2006
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while dressed up in animal costumes, participants grope, fondle, and hump on each other for sexual gratification. no actual sex involved. Usually done in a group setting.
Peter "rabbit" and Jane "cat" fondled each other through their costumes while yiffing at a furry friends party.
by Icerook January 21, 2004
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Young independent Furry.

When a furry is rebellious and declares that he no longer need his parents.
I'm so sick of my parents I don't need them, I'm going to be a yif.
by Kosher Cox May 22, 2017
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the sound that foxes tend to make during sex.
Max and I were out camping and we could hear MTBMichaelR yiffing with a deer that he crippled with Jake Russo's shotgun.
by jakerusso2006 November 22, 2021
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When grown ass men, who live with their mothers and own show cats, dress up in animal costumes and dry hump each other.
jon: "Hey Jimmy do you want to go yiff." Jimmy: No, I don't have time for yiffing. I have to go help mother clean the cat cages."
by H8ing you February 7, 2009
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