Any form of music that is made by nerds, for nerds, or about nerdly things. Nerdcore can be made in any style of music, but most people identify it in either its pop-punk or hip-hop forms. Although many people think the term "nerdcore" was made up by MC Frontalot, it has in fact been in use by rock bands for many years prior to Frontalot's use of the term.

Nerdcore should not be confused with bands that are simply stereotypically popular with nerds such as They Might Be Giants, DEVO, Ween, etc.

Musicians in this genre include (but are by no means limited to):
Rock:
Treephort
Nerf Herder
Warp 11
The Aquabats (definately moreso in their later albums)
The Phenomenauts (Mainly because of their pre-occupation with science)
The Mathematicians
MJ Hibbet

Hip-Hop:
MC Frontalot
MC Chris
MC Lars
MC Hawking
MC Paul Barman
Del Tha Funkee Homosapian (specifically on the "Deltron 3030" album)
Optimus Rhyme
The Lords Of The Rhymes

Electronic:
The NESkimos
The Laziest Men On Mars

Industrial:
Kompressor

Parody:
Weird Al

A lifestyle that inpsired a genre of music which embraces nerd culture, a lifestyle that says you do not need to be ashamed of what you are, if you are a nerd, embrace it and stand proud, change for no one.

One that is at peace with their nerd wisdome and lives their lives accordingly.

Nerdcore hip hop, or geeksta rap, is a subgenre of hip hop music that is performed by nerds or geeks, and is characterized by themes and subject matter considered to be of general interest to nerds, though it can appeal to others as well. Self-described nerdcore musician MC Frontalot coined the term in 2000 in the song "Nerdcore Hiphop". Frontalot, like most nerdcore artists, self-publishes his work and has released much of it for free online. As a niche genre, nerdcore generally holds to the DIY ethic, and has a strong amateur tradition of self-publishing and self-production. The only things required to enter the nerdcore community are a microphone, a computer, and a webserver. No recognized nerdcore albums have ever been released on a major record label, and MP3s, not CDs, are the primary means of distribution.

From Wikipedia

A comical subgenre of rap music which combines the musical style of rap with lyrics about the life of nerds. Often incorporates parody.

NerdCore (adj.): Of genius intelligence with a generous helping of mischief.

something that is simultaniously nerdy yet hardcore, hence nerdcore.