Ima do my very best on this one.
Correct me when wrong.
A timecode dj is a digital dj, that uses special timecode vinyls. These send pulses to the computer, so your computer knows where the needle is. So you can control the computer playing the mp3's with your turntables. In this way, you can play mp3's and still have the feeling of vinyl.
Search 'serato' in google, and read info on their website. You'll find it.