Design pillars
Also said as Pillars, Core pillars
A short list, usually three to five words or phrases, stating what a game must be. Every feature is checked against them, and whatever does not serve one gets cut.
Teams have far more good ideas than they have months. Pillars turn "I don't like it" into "which pillar is that for?", and they decide what gets cut before the deadline does.
Say it
“Our three pillars are fast, brutal and readable. Fishing is lovely and it serves none of them, so it is cut. Let's not reopen this unless a pillar changes.”
Where you’ve seen it
Hugo Martin, who led the design of id Software's Doom games, has described writing down three keywords and using them as guideposts for story, gameplay, systems and visuals alike.
Not to be confused with features
Features are things the game has. Pillars are what those features must add up to. "Crafting" is a feature; "you built this place yourself" could be a pillar.