A WebSocket is a computer communications protocol that provides simultaneous two-way communication channels over a single Transmission Control Protocol (TCP) connection. It is a stateful protocol, which means the connection between client and server will keep alive until it is terminated by either party (client or server). WebSocket is bidirectional, a full-duplex protocol that is used in the same scenario of client-server communication, unlike HTTP it starts from ws:// or wss://. WebSocket is distinct from the Hypertext Transfer Protocol (HTTP) used to serve most webpages, but it is designed to work over HTTP ports 443 and 80 as well as to support HTTP proxies and intermediaries, thus making it compatible with HTTP.

The WebSocket protocol enables full-duplex interaction between a web browser (or other client application) and a web server with lower overhead than half-duplex alternatives such as HTTP polling, facilitating real-time data transfer from and to the server. WebSocket allows bi-directional communication, which means that the client and the server can send data to each other anytime without continuous polling. This makes it particularly useful for building applications requiring instant updates, such as real-time chat, messaging, and multiplayer games.

WebSocket is used for real-time, event-driven communication between clients and servers. It is faster and requires less overhead than traditional API protocols. WebSocket is an essential client-server communication tool that enables two-way interactive communication sessions between client and server without having to poll the server for a reply, providing both speed improvements and real-time capability on the web.

In summary, WebSocket is a protocol that enables full-duplex, real-time communication between a client and a server over a single TCP connection. It is faster and requires less overhead than traditional API protocols, making it particularly useful for building applications requiring instant updates.