So, what is a raw file in layman's term?  raw is the processed recording of what the sensor saw when a capture is made.  This recording is not an image but a latent one a bit like an 'unprocessed slide'. 

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What the sensor records is basic:  Focus (and DOF), luminosity and whatever light artifacts due to the sensor weaknesses (including dust bunnies).   A raw file registers all the camera settings** like focus point, color balance used, flash information and whatever else the camera manafucturer decides.  What it does process is the speed, the DOF, based on the focus point, the gray scale luminosity channels (RGBG) and sadly whatever bias the little manufacturer imp decides to include.

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raw files have the reputation to be dull looking, not anymore.  The change is simply due to the integration of a JPG file within the raw file.  Most image readers access the JPG and ignore the 'real thing' making the display more attractive but highly inacurate.

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raw is usually uncompressed.  When compressed raw is loss-less.

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Then there is sraw for 'small raw'.  That thing was rightly described as 'the evil cross between a raw file and a JPG'.  It retains most of a raw file structure but uses the averaging of four pixels to create one.  Not only the image is reduced in size (both as files space and print size) but it also messes with both color accuracy and luminosity (averaging thingy you know).  To summarize sraw?  A pig with lipstick.

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* Registers, not processes, just in case...