MDA: A game design model
“Mechanics are the various actions, behaviors and control mechanisms afforded to the player within a game context. Together with the game content (levels, assets and so on), the mechanics support overall gameplay dynamics.”
Dynamics describes the run-time behavior of the mechanics acting on player inputs and each other outputs over time (i.e., what happens when people play the game).
Aesthetics describes the desirable emotional responses evoked in the player, when she/he interacts with the game system: sensation, fantasy, narrative, challenge, fellowship, discovery, expression of self, and submission.