Video Games Encyclopedia

An action game is a video game genre that emphasizes physical challenges, including hand–eye coordination and reaction time. The genre includes a large variety of sub-genres, such as fighting games, beat ’em ups, shooter games, rhythm games and platform games. Multiplayer online battle arena and some real-time strategy games are also considered action games.
In an action game, the player typically controls a character often in the form of a protagonist or avatar. This player character must navigate a level, collecting objects, avoiding obstacles, and battling enemies with their natural skills as well as weapons and other tools at their disposal. At the end of a level or group of levels, the player must often defeat a boss enemy that is more challenging and often a major antagonist in the game’s story. Enemy attacks and obstacles deplete the player character’s health and lives, and the player receives a game over when they run out of lives.
Alternatively, the player gets to the end of the game by finishing a sequence of levels to complete a final goal, and see the credits. Some action games, such as early arcade games, are unbeatable and have an indefinite number of levels. The player’s only goal is to get as far as they can, to maximize their score.

Reference: Wikipedia