It's the kreedz of Quake so to speak (but that does not mean it is the same, which it in fact is not). This is the first movie I found on youtube, you will see what it is about
http://www.youtube.com/watch?v=fqq9YcmHW1A
//edit:
DeFrag is a mod that alters, afaik, the movement of Quake3. These things are not possible in standard Q3 what also makes it different from kreedz as kreedz is possible without adjustments.