Someone who you have 'friended' on Facebook but don't really know or keep in touch with. You generally don't know anyone who ever comments on their Wall and wouldn't know them even if they walked right up to you and slapped you.
"Yea, I'm friends with her but we've only met, like, once. She's just a Facequaintance."
Noun. When two people are in the space of time between being acquaintances and friends. Usually occurs after hanging out three or more times, and often results in becoming friends with a "friend of a friend".