When you are talking to someone online, and you both ask a question at the same time, and you both answer each other's question, and you get into two conversations at the same time.
This is normal when text messaging, but annoying when facechatting, hence the name facetexting.
Brad: You going to Tiffany's party?
JayJay: Did you see the Lakers game?
Brad: Yeah that touchdown at the end was amazing
JayJay: Yeah, but I don't think it's gunna be very good. Oh yeah, I punched the air when Tommy Nelson scored.
Brad: It will be good! I'm going. I know right, I punched the air really hard.
JayJay: Stop Facetexting dude!
the act of texting on facebook. can sometimes get to the point of annoyance and fill your friends whole news feed.
jack(to sally on facebook): hey, what are you doing tonight?
sally(to jack): Hey!! :) not to much!! Maybe going out to the bars!!! You??
Jack: Oh I dont know. I dont have any plans:(
Sally: Oh COME WITH US!!!! It will be really fun!
Jack: Oh really? Who is all going?
Sally: Oh EVERYONE!! :):):) Come along!!
Jack: Alright, Ill text you at 8 so that we can stop facetexting.
Sally: Talk to you then.