A collection of remixed top 40 pop songs fawned over by 11 year-old females that discovered the internet, anime, and music the night before. The remixes are created by speeding up any given song to 320BPM and kicking up the pitch enough so that Alvin, Theodore, and Simon froth at the mouth. These songs are always accompanied by a lowres JPEG taken from Fanpop of a random anime girl with no connection to the song and uploaded to Youtube under an account name consisting of a nonsensical Japanese word and a collection of numbers placed there in order to warrant the username available.

Some shit genre that is just a speed up version of songs and therefore takes no talent to make and infringes on copyrights.

As yet unrecognized genre of the music that originated on the Internet, more specifically YouTube. Some people claim to be the creator of it, but since the original account is no longer active (and no one even remembers what was the nickname of the person) those claims cannot be proved.

The main characteristic of nightcore is its high pitch often accompanied by fast beat. Very often songs that were remixed into trance, are later on remixed one again into nightcore and so many nightcore songs have trance-like characteristics.

Even though almost any song of any genre can be nightcored, trance and techno songs, as well as electro music and all types of dance music (here especially eurodance) are most often used. Some rock and pop songs are also nightcored. Rap and metal are the two genres that are heavily avoided, and there are very few songs remixed into nightcore.

A subgenre of trance that has been bastardized in recent year by people who think all nightcore is is a sped up or high pitch version of a song with no further work when in actual nightcore you add original music to the song to make it a nightcore song.

A music "genre" made by a bunch of weebs who think that speeding up a song is considered a genre of music.

It, most of the time is just taking a song and, speeding it up, slowing it down, pitching it up, or pitching it down, with an anime character shown in the video.

On November 6, 2006 a youtube user nicknamed Cuteangel43802 uploaded the AMV called:
Kingdom Hearts: Dont You: Nightcore

And this became the beginning of the nightcore style. The word “nightcore“ was included in the title, as well as under the video as a “music artist“, rather than “singer“ or “group“, and so it was interpreted to be nickname of the person remixing (i.e. high pitching) the song.

Eventually anyone high-pitching the songs would call themselves nightcore (but to distinguish themselves they would add a word, letter or a number before or after the word), and as the amount of people doing it increased, the meaning transferred to the song genre, rather than the person.

Nightcore can include any genre, because the word itself means “high-pitch“, so it is much broader term than “happy hardcore“ and although some “happy hardcore“ songs can be also called “nightcore“, not all “nightcore“ songs can be called “happy hardcore“.

Wikipedia defines “nightcore“ as a name of a band, but whether there is a connection between the youtube nightcore community and the band is unknown. Possibly the name was directly or indirectly taken from the name of the band, but there is no definite proof for this. It may have been as well a coincidence.

A made up genre of music in where an original artists music is sped up an pitched up. Often then released on YouTube or similar sharing site with an anime based video as an original piece giving no credit or royalties back to the original artist. Basically an easy way for some non-talented schmuck to ride the back of a real artists work to gain some kind of notoriety for themselves.