Video Games Encyclopedia

A stealth game is a type of video game in which the player primarily uses stealth to avoid or overcome opponents. Games in the genre typically allow the player to remain undetected by hiding, sneaking, or using disguises. Some games allow the player to choose between a stealthy approach or directly attacking antagonists, but rewarding the player for greater use of stealth. The genre has employed espionage, counter-terrorism, and rogue themes, with protagonists that are special forces operatives, special agents, secret agents, thieves, ninjas, or assassins. Some games have also combined stealth elements with other genres, such as first-person shooters and also platformers.
Elements of “stealth” gameplay, by way of avoiding confrontation with enemies, can be attributed to a diverse range of games, including Pac-Man (1980). Early maze games have been credited with spawning the genre, including Manbiki Shounen (1979), Lupin III (1980), Castle Wolfenstein (1981), 005 (1981) and Metal Gear (1987). The genre became a mainstream success in 1998, with Tenchu: Stealth Assassins, Metal Gear Solid, and Thief: The Dark Project. They were followed by later releases, like Hitman and Splinter Cell.

Reference: Wikipedia