Generally a fraternity or sorority social event when one Greek invites a "crush" to the party. The person invited usually has no idea who sent the invite but will find out at the party. GDIs sometimes get lucky and show up.
frat guy #1 - dude, i just go an invite to a ZTA crush party.
frat guy #2 - who's it suppose to be from, you think?
frat guy #1 - i don't know but there was the girl i met at our band party. could be her.
frat guy #2 - we'll just have to wait and see.