A game engine is the core of a game, a software componant that handles all the necessary technology such as rendering and artificial intelligence (AI).
A game engine is alot different from the game itself, its alot like a car and a car engine, you can take the engine out of the car and build another shell around it and this is what games are like. Today multiple games will use the same game engine.


Unreal Tournament 3 Gears Of War
Unreal 3 engine
Some of the first 2d games include Donkey Kong (1981), Space Invaders (1978), Pacman (1980), Pong (1972)