WebSocket
In plain terms
A protocol for a persistent, two-way connection between browser and server.
Going deeper
Unlike request-response HTTP, a WebSocket stays open so both sides can push messages anytime with low latency. It powers chat, live dashboards, multiplayer games, and notifications.
Under the hood
Upgrades from an HTTP handshake to a persistent TCP connection; needs heartbeat/ping-pong and reconnection logic, and scaling requires sticky sessions or a pub/sub backplane.
Examples
Chat apps, live trading tickers, collaborative editors, multiplayer games, Socket.IO.
Think of it like...
Like an open phone line versus mailing letters: once connected, either side can speak instantly without redialing each time.