When you have a facebook account and someone, usually a signifcant other, or someone that wants to be held in a higher postion in your pecking order feels the need to post, like, or make comments on your facebook page constantly in order to "mark their territory".
Akin to a dog "marking his/her territory" like a fire hydrant with urine.
Dennis: "I hung out with Shannon the other weekend and we had a good time."
Dennis: "But, she's left several comments and posts on my facebook page since then, it's kind of annoying."
Jeremy: "Archetypal facebook fire hydrant my friend..."