Drawn porn featuring furry characters. Extremely repulsive and disturbing to some, exciting and alluring to others.
Animalistic traits refined by evolution serve to compliment conventional human sexiness (expressed in body shapes, facial expressions,
situational context and etc.) resulting in wild variety of lustful self-expression. All genders, sexualities, fetishes and species are present, once you're hooked you'll have a lot to choose from.
Being attracted to yiff typically doesn't mean being a
zoophile since most of such art features humanlike bodies and stylized
muzzles expressing human emotions. That said, there's also such thing as feral yiff.
Lots of people make money drawing yiff comissions but there are also a lot of artists creating such art just for the sake of it. Measuring the sheer volume of yiff content produced daily is currently impossible.
Example:
Alex: my yiff fantasy is that my
jackal fursona is caught between a female fox and a male wolf. She's
foxily slender and has nice hips & tits, he's much more muscular than me and also larger. We're kissing and touching each other, then she lies on her back and I start entering her just as the wolf guy penetrates me while growling in my ear... shit, that's awesome, why can't I draw? Guess I'll commission it.
Some people think yiff signifies our species' growing interest in
transhumanism.