The raw image data from the camera, unprocessed, which allows you to control the white balance, sharpening, and (to a greater degree than jpg) the exposure, in post process.
You can edit RAW files in a number of applications besides CS, including older editions of PS. The catch is that you need the plugin, which probably came with the software bundle or in the case of something other than PS you just need to check the camera support list for that software.