The Hawkins school dance shown at the end of Stranger Things season 2 is called the Snow Ball.
The dance takes place at Hawkins Middle School after the main supernatural conflict of the season. Mike, Eleven, Dustin, Lucas, Nancy, Steve, and other characters attend in formal clothing, giving the season a quieter and more hopeful closing sequence after the danger surrounding the Mind Flayer and the Upside Down.
At the dance, Eleven arrives with Hopper’s permission and reunites with Mike. Nancy dances with Dustin, while Lucas and Max begin their relationship with a dance together. The event provides a coming-of-age contrast to the season’s frightening events and echoes the style of an American school formal from the 1980s.
The Snow Ball should not be confused with a prom. The characters are middle-school students, and the event is a school dance rather than a graduation celebration. It is also different from the Winter Formal referenced in other teen dramas. The scene closes season 2 with the Upside Down looming over a vision of Hawkins, suggesting that the danger has not truly disappeared.