any extended period of leave from one's customary habit of always being on facebook, absorbing more meaningless drivel from people you haven't missed for years but are now somehow your FB friends, for the purpose of performing work, getting rest or to acquire new skills or training, etc. In other words, to get a life.
a rest from logging on/using Facebook that could last for a week to a month. The user will stay facebbatical until something new and eventful thing happens in their life.