Save system
Also said as Autosave, Save points, Saving, Save slots
The rules for how your progress is kept: whether by save points, by saving anywhere, or by autosave, where the game writes your progress for you every so often. Each choice sets what a mistake or a crash can cost.
It decides how much a player has to lose, and so how brave they're allowed to be. It also has to work: a crash that costs an hour of play is what people remember, and a lost save can end a game for them.
Say it
“Autosave on every room change and every 60 seconds at most, keep the last three in rotation, and show a small icon so that people know not to switch off.”
Where you’ve seen it
The first Resident Evil makes you spend an ink ribbon at a typewriter for each save, so saving is itself a decision. Dark Souls autosaves constantly in one slot, so you can't reload your way out of a mistake. Breath of the Wild keeps a number of autosaves alongside a manual slot.
Not to be confused with checkpoint
A save keeps your progress between sessions. A checkpoint is only where you come back after dying, and it may never be written to disk.