HDR imagery is an image with at least a 12 stop range. SLRs unfortunately dont have the potential to produce that depth in tone so therefore the technique involved is called 'tone mapping' or LDRi (Low dynamic range imagery). Our eyes are great examples of how huge tonal depths can be balanced 8) But yes true HDR is comprised of multiple images at multiple exposures, only it would have a much wider range. LDR can be achieved via a single RAW format exposure or a couple of frames at say -2EV, -1EV, 0EV, +1EV, +2EV. Theres been a whole load of media hype making any shot with the slightest (and usually too much) tone mapping considered an HDR image, but its simply now true :-/