I saw someone describe this very efficiently once on a gaming subreddit. I don’t think it includes the term ‘hard-coded’ though I suppose that could work.

For example, natural synergy in a game might be that a sword and shield pair well together because you can use one hand for the sword to attack and the other to defend. The type of synergy I’m talking about, though, would be like if some knight’s sword had a stat that made it deal 50% more damage per attack if paired with the shield owned by the same knight, but deals ordinary damage if used with any other shield.

The idea is that it may be poor game design if done too frequently because it takes away opportunities for players to be creative with how they combine weapons/equipment/etc and what cool synergies they might discover naturally. There’s less fun in mixing and matching when the game developers already did it for you.