WebSocket is a part of the upcoming HTML5 web standards. It allows a web browser and a web server to have a persistent, two-way full-duplex connection using just one TCP connection. It does this by starting a regular HTTP connection and then effectively renegotiating it into its more flexible underlying TCP connection. This gives it good chances to traverse firewalls, effectively giving us back the full power of the Internet.
In this way, it is an evolution and replacement of Comet, which is a collection of hacks to use Ajax to simulate persistent HTTP connections. WebSocket improves over Comet by being standardised, much cleaner and more scalable. It does, however, require explicit support by both the server and the client. Currently, only Chrome 4 has WebSocket support. It is planned for Firefox and Safari. The latter means the WebKit rendering engine and that means WebSocket can be ported to Syllable's browser Webster.