The act of Liking your friend's status on facebook as a show of thanks for them liking yours. This can also be done with people you don't know who like your status and or links or other posts. People could also refer to this as just Facebook Manners.
"____ Likes your status."
Your Friend: "I didn't know you were friends with ____?"
You: "Oh, I never talk to them. I'll just Like-Tag their page and we'll call it even."