What is the name of the school dance where Rory and Dean kiss in season one?

The school dance where Rory and Dean kiss in season one is the Chilton Dance.

Rory attends the Chilton dance with Dean Forester during the first season of Gilmore Girls. The event becomes important because Rory and Dean's relationship develops while Rory is adjusting to her new private-school environment.

The dance also highlights the social contrast between Rory's Stars Hollow life and Chilton's more formal student culture. Paris Geller and other Chilton students are part of the school setting, while Lorelai becomes involved in the evening's events as Rory's mother.

The event is commonly remembered as the Chilton dance, although episode listings may identify it through the episode title rather than treating the dance as a separate named festival. It should not be confused with Stars Hollow community celebrations shown elsewhere in the series.