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 27, 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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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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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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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 21, 2017
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Unidentified substance found at the back of a fridge/ car boot/ toxic waste depository that will
make a great bet if you ask someone to drink it.
"In further news police have seized 70 tons of yif from a prominent drug cartel"
by Toasttheoverlord January 24, 2019
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