Nightcore can refer to:

Nightcore by littlekuriboh500-d5to9vv
Nightcore (group)
Nightcore (genre)

As a group: Nightcore was a group consisting of Norwegian DJs Thomas S. Nilse and Steffen Ojala Søderholm who kickstarted nightcore edits sometime in 2002.

As a genre: A nightcore edit is an edit to a song that speeds up and increases the pitch of the original song. This form of music was made back in 2002. Fans of this music usually refer to it as "happy hardcore". This style originally started as a subgenre of trance but later evolved to be the music we know today.