your guest when you are invited to an event

I couldn’t care less (but one must keep up appearances, right?)

Accompanied by a guest.

At public parties and nightclubs, the guest of a person who is on the guest list, and who normally pays a discounted entry fee. Also, the state of having such a person.

Usually written '+1', used in a forum post to indicate that the post serves no purpose other than to increase the poster's postcount. Usually used after an empty post along the lines of 'I agree'. Often used in a sarcastic manner to indicate the pointlessness of the entire thread.

(noun) - the person who is invited to join an existing coupled unit in sexual activity resulting in a three way or menage a trois. Depending on the genders and desires of the couple, the "plus one" may even become a lucky pierre.

n., a person who sleeps with (and therefore enjoys many of the social priveledges administered to) an entertainer, especially a Disc Jockey