3 terms
Game mechanics are the rules and systems that define what players can do in a game, how the game responds and how actions lead to outcomes.
A gameplay loop is the repeating cycle of actions, challenges and rewards that a player performs in a game, forming the core of its moment-to-moment design.
Level design is the game design discipline of building playable spaces, arranging layout, challenges, pacing and guidance so players learn and enjoy the game.