Yiff

Yiff is an onomatopoetic word and/or sound, coined in 1990 by Foxen while roleplaying his fursona, littlefox, originally to meaning a cheerful greeting or an energetic "yes", but changing over time to be used more commonly as an expression of sexual interest or activity.

A very common word in furry lore, it can be used as an interjection, an adjective, a verb, or a noun.

History
In Foxish language, yiff initially meant "yes!" or an enthused "hello!". Later, "yiff" was assigned a more sexual connotation, a meaning that had previously been assigned to yipp (a coarse form of yip). This was compounded by several fox characters on Furry MUCK who were spreading a very sexual reputation for the species at about the same time as this came into common usage.

Alternative term use

 * As a furspeak or furry version for the English profanity word, Fuck ("Ah, yiff that!" or "Yiff You!").
 * To express happiness, success, or feeling ("Yiffy").
 * To describe erotic, sexual, or pornographic anthropomorphic media (noun).
 * As a descriptive acronym (YIFF or Y. I. F. F. - "Young Incredibly Fuckable Furry").

Yiffing
Yiffing is a term for sexual intercourse between furs.

Origin
The exact time the term "yiffing" was coined is disputed. The most popular etymology stems from the 1980s, citing that "yiff" was the sound foxes make while mating.

Euphemisms
Yiffing comes with its own set of sexual euphemisms, in addition to many of the same slang terms used in human sex. For example, a popular term for male masturbation is "pawing off" ("clopping" within the My Little Pony: Friendship is Magic fandom, specially by bronies). .