Not "quite" correct, HDRI (as used in rendering terms) is a subset of image-based lighting that can have brighter than white lights and darkere than black shadows. This is so the renderer can determine the lighting difference between a sheet of paper, a phospherent light, and the sun. The reason I say this is "not quite right" is that you can have greater than eight bits of colour information and NOT be uing HDRI. For example, using 16 bit tiffs would still be classified as non-HDRI.