Stealth is a combat skill that determines how effective a player is at remaining concealed whilst moving. During stealth the player has reduced movement speed and has a green bar that once depleted will cause a reveal. While moving the player can also be revealed even without the bar depleting, as is skill failure. Standing still in hiding will replenish the stealth bar allowing for longer periods in stealth. It relies on the Hiding skill. Skill gains will only be accrued while moving in stealth, while the act of entering Hiding will contribute to the Hiding skill.
The current maximum of distance that you can travel is based off of your stealth skill. Even at 99 Stealth you have a chance to pop out of stealth immediately; however, generally can travel further distances as stealth raises. Once you reach 100 stealth the only way to be revealed is by running your green stealth bar to nothing, someone got directly on top of you and hit you, get hit by AoE (Area of Effect) abilities, come in contact with the spell Ward: Hidden, or perform an action that reveals you.
The following NPCs can train your stealth skill to 30 for 300 :