From Seo Wiki - Search Engine Optimization and Programming Languages
SPDY, pronounced "Speedy", is an application-level protocol for transporting web content. It is a proposed replacement for the HTTP protocol and created by Google.
The goal of SPDY is to reduce web page load time. This is achieved by prioritizing and multiplexing the transfer of several files so that only one connection per client is required.
All transmissions are SSL encrypted and gzip compressed by design (in contrast to HTTP, the headers are compressed too). Moreover, servers may hint or even push content instead of awaiting individual requests for each resource of a web page.