Sex, slang for sex. Usually used when someone doesn't want to type sex or when there parents or someone they don't want to have seeing what they are writing is around. Also could be a typo when trying to write sex.
Bob:
Haybabe whats up, wanna do the deed later?
Bill:
You got the wrong number dumbass Bob:
Woah your not Janet
Bill:
I am not in deed, and i sure as hell aint having sx with you tonight either.