SPDY is a transport protocol created by Google.

The reason for its existence is the shortcomings and inefficiency of HTTP/1.1.

Today, SPDY is no longer relevant, as all of its capabilities have been “transferred” into the new HTTP/2 specification which is seeing positive adoption around the web.

SPDY is less of interest in the context of WebRTC, where optimizations of performance for signaling tend to use WebSocket instead.