To Remove inferior and useless friends from one's Facebook friends list. Typically fake friends and fremies who one doesn't want stalking them are removed.
Either the verb (to cull) or the acronym CULL (C U Later, Loser). Typically used when reverting your friends list on facebook to contain only those people you actually know and talk to.
Some of my so called friends on facebook only sent me an add to bump up their numbers - CULL time!!
All that girl does is whine on her status every 5 minutes, clogging up my home page. She needs culling!