Shadow stealth is basically a line of sight system
that involves the shadows, in which we can hide ourselves in the dark zones which hides the player more efficiently. This system is used specifically when games are set at night times, however most of the games missions take place at night. When the player is in a lighted zone he may use the same techniques while he uses the line of sight stealth
system. Some shadow stealth games allow the players to break lamps, turn off lights, extinguish torches and other such things to generate shadows to allow the player to pass through, even under the enemies sight; this adds a certain diversity in the level design since the player doesn't have to always use obstacles to conceal themselves. The subtlety of this system is made by the fact that the shadows can conceal ourselves more or less efficiently in regards of the enemies. The darker the shadow, the more concealment it give us and lets us get much more closer to the enemies sight without being detected. The more silent we are will get us less enemy attention and helps us not take the risk of being detected.
The Shadow meter
This meter tells the player how concealed he is in the environment. It also shows how obvious the player is when around enemy sights. The more the player is concealed the higher the meter will rise and the more open the player is the meter will lower. One of the first games to utilize this game mechanic is the game: Thief: The Dark Project