Game state
Also said as State, World state
Everything the game needs to remember at this moment: where each thing is, how fast it is going, whose turn it is, who is alive. All else can be rebuilt from it.
Saving, loading, replays, undo and online play all depend on knowing exactly what the state is. A value left out of it becomes a bug that only shows up after a reload.
Say it
“Keep the whole game state in one object: positions, speeds, health and timers. Saving is writing that object out, loading is reading it back, and particles are not part of it.”
Where you’ve seen it
A chess position is a full game state you can see at a glance, plus a little you cannot: whose turn it is, and whether castling is still allowed.
Not to be confused with save file
The state is everything in play right now. A save file is the part of it you wrote down, and it can leave out what can safely be rebuilt.