Shred is to guitar what extreme sports (bungee jumping, sky diving...) are to sports in general.
Shred involves faster, harder to play stuff and some show off attitude that you won't find in other styles, where the main goal is somewhere else, (usually it's creating art).

When we talked about how dangerous shred was, it was how you could develop tendinitis due to extreme practicing of scales, arpeggios etc. at an extreme speed.

Artists like satriani and Vai are said to be shredders, but they actually have a style that involves more than just shred. Shredders are far more extreme than Vai or Satch when it comes to chops. You can find some names in the 'famous bands and artists' under 'fastest guitarist you know'...