Snapshotting refers to mechanic involving Tiger's Fury and Bloodtalons, that will confer the damage increase to the entire Bleed DoT effect if these buffs are present when you apply them. This is specific to these two effects, and does not apply to things like trinkets or dynamic buffs such as Savage Roar. This means maintaining Bleeds with these effects up is very important to making the most out of them, and ideally you want to make sure Rake is buffed by Tiger's Fury, and Rip is buffed by both that and Bloodtalons if taken. You should also try to minimize the number of times you overwrite these effects without these buffs present.