Definition of "yiff"
yiff
/jɪf/
noun
usually uncountable, plural yiffs
(slang, informal) Sex, especially between furries (fictional anthropomorphic animal characters, and/or members of the community surrounding their celebration).
(slang, informal) Pornography of or involving furries.
verb
third-person singular simple present yiffs, present participle yiffing, simple past and past participle yiffed