Mechanics are the formal rules and algorithms that govern a game — what a player can do, under what conditions, and with what outcomes. In MDA, mechanics operate at the level of data representation: the precise, engine-level definition of the game’s state and the functions that transform it (Hunicke, LeBlanc & Zubek 2004, see source-mda).
Contested usage: Schell uses “mechanics” more broadly to include goals and progression alongside rules (Schell 2008, see source-art-of-game-design). Adams treats mechanics as the formal system but distinguishes them from the game’s presentation layer. The MDA definition is narrower and more analytically useful when reasoning about emergence.
Related: mda-framework, dynamics, internal-economy, game-atoms, systemic-depth-elegance