It's like seeing a picture of Zac Efron and you go UNFFF

so is it like a sound or it means something?

It's a sound like nnn;;

I don't even think it's a sound. I tried to sound it out so many times before and I sound foolish lmao. But yea it's like a... "word" you use to explain your sexual desire. Imagine you're texting and someone sends you a hot pic of a celebrity you crush on and you reply like "UNFFFF".

I don't and never will use it

"Universal Noise of ****ing" = UNF

It's a sexual moan. That's all
/endthread

This.

The sexual noise you make when you're enjoying it. It's like the classier way of saying "YES! GIVE IT TO ME LIKE THAT!"

Technically it's a literal acronym, as posted above, but most people pronounce it as just a noise or moan. Essentially it means the same thing. Basically just something used when you see a picture of or talk about someone you find attractive.