Interest management
The practice of sending each player only the parts of the game state relevant to them, so bandwidth doesn't scale with the size of the whole world.
In a game with a thousand players no client can receive updates about all thousand every tick — bandwidth would explode and most of it would be invisible across the map anyway. Interest management (often "area of interest", AoI) filters state per recipient, usually through a spatial grid or zones where the server only replicates objects near the player.
The idea is as old as networked games themselves — Tribes described its priority-based scheme in 1999, and Unreal calls it "relevancy". It plays into snapshot interpolation and client-side prediction: less data to send means what is sent can go out more often. The awkward case is objects right at the edge of perception, which have to fade in without popping.