Non-stop running games are defined by two things: The player-controller avatar cannot stop its forward momentum, and it has feet. Games that reward or celebrate speed such as ones in the Sonic franchise are spiritually similar, but subscribe to a different philosophy. It also excludes games where the player would ideally always be running such as Mirror's Edge, as stopping does not necessarily introduce a fail state. This also excludes games that use the mechanic of forced motion only during sections of gameplay, such as the Crash Bandicoot escape sequences, or the brain worm sequences in Limbo. Note that just because a game is classified as Endless Runner games in this category aren't all necessary endless. For instance Rayman Jungle Run and T.E.C 3001 both are considered endless runners although both are level based with a clear end state.
Generally presented as a 2D side-scroller, although titles like Fotonica still maintain the concept in first-person 3D. Controls are generally simple, focusing on actions such as jumping over obstacles, although melee and gunplay are not out of the question. Success or progress is usually measured in distanced traveled without dying or crashing.
Games featuring this concept tend to appear more frequently on mobile platforms such as iPhone or Android since simplified control schemes lend themselves well to one-handed gaming.
Ancestors of the endless-runner genre include the early endless scrolling platformers Jump Bug (1981) and Moon Patrol (1982), the third-person special stages in Sonic 2 (1992), and the Sega Master System version of Aladdin (1994).