Youll find the terminology of "stages" used to descibed cams in every single motor ever built.

Its just an easy way to describe how much more aggresive over stock they are. Normally they go in 3 stages.

Stage 1 is a street upgrade, basically a little bit more lift, a little bit longer duration, adds a few more HP and a bit more torque without the need for tuning, and without making it totally unstreetable and shit on fuel, a pig in traffic etc.

Stage 2 is for those who track their cars often, a weekender or once a month car, but still needs to be reasonable in traffic, and on fuel. Duration and lift are increased a bit more, generally helps to have something to tune to, and you wouldnt do it without having all the supporting mods, intake, exhaust etc

Stage 3 is generally regarded as race only. Massive lift, longer duration, moves the power well up in the rev range, results in the under lump idle, shit on fuel for daily driving. Really only useful with a complete aftermarket computer, all external mods, and internal stuff, valves, valve springs, retainers, all upgraded.