Re: Questions about shredding?
Tremolo picking is when a guitarist imitates the way a mandolin is picked. Your left hand is playing quarter notes, for example, and your right hand is picking them as 16ths.
"Shredding" can apply to any fast, technical playing. Some shredding is done with very few strokes (arpeggios, sweep picking), and good portion of it is done with some combination of alternate picking and legato technique (hammer on/pull off).
Another technique is called circular picking. And don't forget two-handed tapping!!