Prom Dating 

(n.) the condition of a semi-forced, semi-serious relationship resulting between two people who are going to prom together. This normally includes texting, brief hangouts, and any other activities that would "set up" the night of prom. Normally, such a relationship lasts from the instant when the dates decide to go together until the morning after prom.

Person 1: Hey so are George and Stacey together?

Person 2: No, they're just prom dating.

Prom Dating by Praerk May 1, 2010

Promdating 

Used when two people are not in an actual relationship but are going to prom together.

Are those two dating? No, they're just promdating.

Promdating by AyBayBay10 May 12, 2011