Platform games task the player with directing their character to jump, climb, run and avoid obstacles. Getting their name because of levels constructed of platforms from which you have to jump, these games usually introduce hazards to make the forward progress more hazardous.
Although often played with just a joystick and couple of buttons the timing and duration of the button presses and joystick direction requires considerable skill. When combined with Simulation genre the character responds to the physical mechanics of the game world in such a way that players need to spend time learning to use their instincts and relations to progress.
These are commonly considered Action games, but platformers (as they are often called) can also be combined with Fighting or [link to search/genre/Rhythm/ Rhythm games to create a wide range of ways (and reasons) to traverse levels. Although Platform games are usually simpler to understand. However, when combined with Open-World or Puzzle genres they can present a larger and more complex challenge to players.