The level to which a game’s component parts are designed with the whole in mind. That is, how well each aspect of a game (art direction, mechanical systems, story, animation) click together to reinforce the intended ideas and experience. It’s worth noting that a game can have deliberate or accidental synergy.

“Escort missions cause most gamers to recoil in horror, but the synergy between the narrative of reluctant protector Monkey and the systems which require Trip for the player’s literal survival in Enslaved neatly sidesteps the psychological issues.”