The Rice University Neologisms Database

stands for "facebook official", means when two people's relationship is posted on both of their profiles. In middle school, a relationship is not real until it is fbo. The purpose of posting these updates was that people that had significant others could brag about it without actually bragging. People in high school and older use fbo in a more sarcastic way, because the need to flaunt one's relationship is then seen as childish.