http://dev.chromium.org/spdy/spdy-whitepaper

The SPDY project defines and implements an application-layer protocol for the web which greatly reduces latency. The high-level goals for SPDY are:
To target a 50% reduction in page load time. Our preliminary results have come close to this target (see below).
To minimize deployment complexity. SPDY uses TCP as the underlying transport layer, so requires no changes to existing networking infrastructure.
To avoid the need for any changes to content by website authors. The only changes required to support SPDY are in the client user agent and web server applications.
To bring together like-minded parties interested in exploring protocols as a way of solving the latency problem. We hope to develop this new protocol in partnership with the open-source community and industry specialists.

Some specific technical goals are:
To allow many concurrent HTTP requests to run across a single TCP session.
To reduce the bandwidth currently used by HTTP by compressing headers and eliminating unnecessary headers.
To define a protocol that is easy to implement and server-efficient. We hope to reduce the complexity of HTTP by cutting down on edge cases and defining easily parsed message formats.
To make SSL the underlying transport protocol, for better security and compatibility with existing network infrastructure. Although SSL does introduce a latency penalty, we believe that the long-term future of the web depends on a secure network connection. In addition, the use of SSL is necessary to ensure that communication across existing proxies is not broken.
To enable the server to initiate communications with the client and push data to the client whenever possible.