What is WebSocket?

WebSocket is a communication protocol that opens one connection between the client and the server and keeps it open. Once the connection is up, both sides can send messages at any time, in either direction. (A protocol is an agreed set of rules for how two computers talk to each other.)

Regular HTTP is like exchanging letters: you write, you wait for a reply, and you write again. A WebSocket is like a phone call: you dial once, the line stays open, and both people can speak whenever they want. This ability to talk in both directions at the same time is called full duplex.