Whats the intensity value in the EXIF data?

As above, I would like to know what this value stands for. The more light, the larger value? or is it the difference between the darkest and the lightest part of the pict, has it to do something with the dynamic range in the pict? This "intensity value" can be found in the EXIF data in the META data panel. It is rigth above the expo compensation.

Thanks: Imre