Most high end cameras have the capability to shoot in RAW. Now, if you've never heard of RAW before it's a really marvelous thing for photography. What a RAW file essentially is, it's very similar to a JPEG file, but instead of just saving the single exposure that you shot it saves a full range up and down below that exposure. So, you have the ability after the fact to edit the image with actual data instead of just manipulating pixels.
For example, if I shoot a photograph at 1/60 second, f 2.8, ISO 400, when I shoot a JPEG I'm just saving that specific image at that specific exposure. However, if it's a RAW file it's going to give me way up and way below. The same thing goes for the white balance of the image. This basically means if I shot a photograph, let's say outdoors, and my white balance was set to indoor lighting, everything's going to look really off. It's going to look really yellow. However, thanks to RAW processing, and we'll get into RAW processing programs, I can go back and correct that with physical data.
Most cameras have their own proprietary RAW extension. So, it's never going to be thefilename.RAW. It'll be something like .NEF, .DNG, .CR2. Basically these can all be converted down once you start processing them, and saved as TIFF files. Layered TIFF files, much like JPEG files, can be universally read by most computers and most editing software. The nice thing about a TIFF file is as you work with it it saves much more data in that file than a JPEG would.
So, whenever shooting an assignment I, without question, will always put my camera into RAW. Because, obviously, the goal is to get the right exposure and the right white balance the first time, however nobody's perfect and nobody can take into account extraneous factors. It's just nice to have that as a backup. Of course the file size is going to be a lot larger, and it's more data you're processing, but the payoff is much higher, too.
And that's everything you need to know about RAW.