Silly side terminology...
Say you're married and have a partner outside of wedlock.
You're spouse's parents are your "inlaws"
Which makes you're partner's parents your "outlaws" hehe!
Not that you would ever call them that to their faces...or that parents really need to know what's going on...but somehow even my 87 year old grandma instinctively knows to introduce my man as my "friend" and not my "boyfriend."
We mostly use "friend" or "partner" in public because we work together and we try to separate our private and professional lives ("partner" often takes on the sense of business partner and since we're in the entertainment business it's better for business if audiences think that both single).
However I'm not fond of "partner" on a personal level because I want something that's not so neutral, I want to expresses my femininity and his masculinity. We never use "girlfriend" or "boyfriend" because to us those terms implied exclusivity. Also if we're out at a bar and he's trying to flirt with a pretty girl and someone swings up and accidentally calls me his "girlfriend" then pretty girl gets all confused and is afraid to flirt back...
Haven't really found the best labels yet. Some that don't really apply to me but that may be fun: