|80/100 giving extra checks?||yes|
|Obtainable in game?||yes|
Stealth is a passive skill that increases the likelihood of hostile monsters not attacking the PC on sight (until provoked).
This skill prevents some monsters from noticing the player character. If you are very good at it you might be able to sneak past monsters or mount a surprise attack. The Stealth skill also is extremely helpful in ambushing monsters in the wilderness. In that special case it can be supplemented by the Survival skill.
With high Stealth, monsters that are guaranteed to be generated in a particular pattern (e.g.: the steel golems in Darkforge and all monsters in D:50), or that appear in vaults, may just stand still until the PC comes very close to and/or attacks one of them.
Stealth reduces the chance for Shopkeepers to notice an invisible PC picking up items from their shop.
Stealth also increases the likelihood of the PC "sneaking up on" monsters encountered in the wilderness, allowing the PC to ambush them or to evade them more easily. As the manual points out, the Survival skill also gives a chance to ambush monsters in the wilderness.
If the PC has the Stealthy talent, a extra check to this skill is made when monsters are generated (on top of the extra checks gained at skill levels 80/100).