When you get a friend request on facebook and for whatever reason you feel obligated or feel it necessary to accept their request even though you would prefer not to.
See facebook friend snare
I didn't much like Lisa when we worked on the fundraiser together and now she put in a friend request to me on Facebook. I wouldn't have accepted it but she is so well connected in the community I think it would be a mistake to ignore it. I grouped her under what she is--a Facebook obligate friend.