Stealth is a mechanic in Paladins that allows champions to turn invisible to the opposing team. Taking damage or performing actions like weapon attacks or casting abilities will break stealth, making the champion visible again. Enemies moving too close to an stealthed character will cause it to become partially visible. There are also several Cards that allow champions to diminish or disable the effects of stealth.
Skye is a champion who has the ability Hidden, which allows her to become invisible for a duration. She also has certain cards that can enhance this effect, or even allow other of her abilities to interact with it.
Stealth Grass allows any champion to turn invisible while inside them until they perform an action, a member of the opposing team enters the bush or they leave.