Friend or relative you always see also in "Common friends" section of facebook and you can't figure out how can they possibly know each other.
On facebook everybody knows Alex. Must be Facebookcentric.
2. (there is already one definition published, this is another) (adj.) describes an exchange of information, be it person-to-person, news media-to-person, social media-to-person, that involves Facebook in any overt way.
A recent facebookcentric article was on CNN.com outlining the "12 Types of Facebookers."