noun: An invitation to something where the inviter already knows there's no way the invited can possibly make it. That way he still gets credit for pretending to want to hang out with them.
verb: The act of inviting a person to an event, knowing full well that that can't make it, when you didn't really want them to go anyways.
noun: "Yea, I got the 'unvite' again from Shane. He knows I can't possibly go to Halloween Horror Nights this weekend, what a douche. Then he acts all upset that I can't make it. He's such an ass."
verb: "Philip has to study for a final tonight, so he can't go. Prolly I'll unvite him anyways. That way I still get credit for asking him to hang out"
Sending an invitation very last minute with the hope invitee will already have plans. Unvites are used when you do not want someone to attend but NOT sending them an invitation would be rude.
According to Seinfeld episode 908 (The Betrayal), an unvitation (sometimes spelled un-vitation) is when you send someone an invitation to an event knowing that the person will not attend. Unvitation are usually sent for events in which the invitees give gifts to the inviter (a birthday or wedding for example). The hope is that the people who can’t attend will feel guilty and respond by sending nicer presents.
Billy: How come you get better birthday gifts from your Grandmother then I do?
Bobby: Because my Grandmother lives 3,000 miles away and I always send her an unvitation to my birthday party.