RAW is (rather unfortunately) also a name for two or more file formats.
RAW picture files: I have found them defined as "PSD without a header" - and also as file formats that simply list the RGB values of the pixels in an image according to some trivial ordering.
My current impression is that inside a .raw file you may find just about anything including a rubber duck.
In digital camera jargon, a RAW file is a file that reproduces as closely as possibly what comes off the CCD (or CMOS) of the camera, without any attempt at compression, color correction or other manipulations.
This is often desirable, because many cameras are able to generate RAW files at 12 bits per color channel (making a total of 36 bits per pixel), as opposed to the 8 bits per channel that JPEG imposes.
RAW sound files: unfortunately, the same extension and name is also used for sound files. I believe that a .raw file is simply a sequence of samples without a header that describes their format.
Guessing the sampling frequency and the sampling amplitude (8 bits, 16 bits ...) is lefts as an exercise to the user.
practically speaking: if you have a .raw file do not bet your job on its portability.