Host migration
The mechanism that lets another player take over as server when the host of a player-hosted match disconnects.
On a listen server or in a P2P setup, the authoritative game state lives with a single participant. Lose them and you lose the match — unless the others already hold a copy of the state and have agreed on who is next in line. The game freezes, the chosen client spins up a server from its local state, and everyone reconnects to it.
Call of Duty: Modern Warfare 2 (2009) made the "Host migration" screen part of daily life for millions of console players. It is rarely seamless: whatever happened in the last hundred milliseconds before the drop can be lost, and the new host may well have a worse connection than the old one. Dedicated servers make the whole problem go away.