I think this is a fair question. I myself have no family or coworkers on FB friend list, just friends who would honestly care and want to share in my life.
As for an answer to the original poster, I really don't know. I don't have titles or categories---just a lump sum of friends. My relationship status simply says "In an open relationship" but I left out the with whom part. (But thanks to various posts & photos on my wall, everyone should know who it is.) It works for my purposes.