What is nightcore....?

Ahh nightcore, I love it :D

Well there are two types of nightcore
(The Examples are my personal favorites when it comes to nightcore)

Type 1 (Most Common)- Speed up the song and boost the bass a bit
http://www.youtube.com/watch?v=dV_m1H3hDio

Type 2 (Rare)- An actual remix that goes good with the classic nightcore taste
http://www.youtube.com/watch?v=jOb99L610Vk

(If its not fast, and if the bass isn't kicking, it isn't nightcore)

It's simply a sped up (therefore also increased frequency/pitch) version of a normal song. Yes, there are some actual night core remixes, but 99.9% have just had their tempo raised in a simple audio editor like Audacity.

"Nightcore", the glorified term for speed up techno/trance/dance songs.
bit.ly/whatisnightcore and knowyourmeme.com/memes/subcultures/nightcore

Dude I have that same link you provided in my youtube favorites list. I love this stuff.
And the other peeps are right about what nightcore is.

It's a ridiculously fast paced techo-ish thing. It's a bit hard to explain in other words, but that's the gist of it. It usually has heavy drum and bass lines, as well as a tendency to soing noisy. Usually not in a bad way.