This entails: two friendly friends who hook up to realease sexual tension as a favour to each other.
This short form is usually used in textual messages, by teenage girls, and lazy people who do not like the sound B makes.
See also, fuck buddy.
Aaron: Sure, lets get our horny on!
Pam: Awesome, I could really use some friendafits, most deff!
Tony: NO, they are just Friend-a-fits.