Rapid Start is an Intel technology aimed at allowing systems to resume from deep sleep in 5~6 seconds. Intel Rapid Start Technology is designed to provide a faster resume time than traditional suspend-and-resume methods, maintain user contexts, and is much more efficient than handling a full shutdown/start-up process.
At a technical level, Intel Rapid Start comes down to the firmware just copying the RAM contents to a special on-disk partition and then during the resume process to put the partition contents back into RAM.
Matthew Garrett has been exploring how to support this under Linux and has been making progress. He now has a kernel patch that might be merged for Linux 3.11 that allows for setting the bits dealing with Intel Rapid Start. Aside from the kernel handling, there's also some user-space implications currently being explored for setting up Rapid Start on Linux desktop systems.
More information on Matthew's Intel Rapid Start for Linux exploration can be found via this blog post.