Invisibility is a state that bonuses stealthy actions which scales with your Stealth ranks and stacks with other buffs to the Stealth skill. The potency of the bonus to stealthy actions varies with the potency of the effect, although since each stealth action treats invisibility in different ways this variability differs from one ability to the next and in some cases invisibility is just a binary condition to the stealth action. The condition of being invisible, as well as providing a general bonus to stealthy actions, enables the person to do certain actions (like moving from room to room or removing/wearing items) without a skill check or roundtime at all.
For the purposes of HUNT or SEARCH invisible individuals may still be detected and revealed. Most abilities which provide invisibility will eventually "pulse" though, putting the user back into that state without their intervention.
Abilities that give invisibility