HTML5 WebSockets, defines a full-duplex communication channel that operates through a single socket over the web. WebSocket is not just another incremental enhancement to conventional HTTP communications, it represents a large advance, especially for real-time, event driven web applications.
Normally when a browser visits a web page, an HTTP request is sent to the web server that hosts that page. The web server acknowledges this request and sends back the response. In many cases—for example, for stock prices, news reports, ticket sales, traffic patterns, medical device readings, and so on—the response could be stale by the time the browser renders the page.