Wikipedia
SPDY (pronounced speedy) is a now-deprecated open-specification networking protocol that was developed primarily at Google for transporting web content. SPDY manipulates HTTP traffic, with particular goals of reducing web page load latency and improving web security. SPDY achieves reduced latency through compression, multiplexing, and prioritization, although this depends on a combination of network and website deployment conditions. The name "SPDY" is a trademark of Google and is not an acronym.
Throughout the process, the core developers of SPDY have been involved in the development of HTTP/2, including both Mike Belshe and Roberto Peon. In February 2015, Google has announced that following the recent final ratification of the HTTP/2 standard, support for SPDY would be deprecated, and that support for SPDY would be withdrawn. Google removed SPDY support in Chrome 51.