"Core mechanics" refers to the fundamental rules and actions that make up a game or activity. It is the essential gameplay that drives the experience and defines how the game operates. Full definition
«I am still very much for removing combat as core mechanic in horror games,» he said. (waypoint.vice.com)
Not to be too outdated with core mechanics, the game features an RPG - like progression system. (dualshockers.com)
As a beginner, I did not feel overwhelmed, with the in depth tutorial taking me by the hand and gently guiding me through the games core mechanics. (thevitalounge.net)