Its hard to define shred. Technically speaking, (note-by-note) a chord is the fastest flury of notes. It so fast, that it sounds like one note. Yet, we all know that we stum down or up which causes tiny miliseconds between each string.

...and by goin by raw definiton, a chord is the fastest way of playing notes. BUT!!!, no one thinks of that as shredding.

Its hard to define is cause there are no real guildlines to go by. In the 70's shredding was Ace Frehley, Jimmy Page. In the 80's it was Van Halen, Malmsteen, Kirk Hammet, and every Hair metal guitarist. In the 90's it was like John Petrucci, Micheal Romeo, Stevi Vai.

And now in the 2000's, we have people like Rusty Cooley, Ferrai, and sickly fast people who when we hear them, we would never never conider a person like Van Halen to be in the same category.