HTTP compression is defined in RFC 2616 specification as a negotiation between the Web browser and the Web server. If a Web browser sends a request with an "Accept-Encoding: gzip" header to the server, it tells the server that it understands compressed (encoded) responses. If the server is capable of sending compressed data, it marks its response with a "Content-Encoding: gzip" header. When a Web browser receives data from a server with this header information, it decompresses the data transparently and displays the uncompressed content.
HTTP Compression saves transfer data volume and speeds up Web page load time.