Sneak
From AoP Wiki
Sneak is a possible secondary Skill you can level up during gameplay.
It's starting value is:
Being a secondary skill, it can be leveled up to 200%.
Each % decreases the distance you can be spotted when in Sneak. You can not Sneak when you have less then 100%. In addition to that, you are required to have one of three types of Stealth Boys equipped, in order to Sneak.