HDR (high dynamic range) is basically when you shoot the same scene with 3 different shots; 1 at normal exposure, one at a lower exposure, and the third at a higher exposure. You would then combine them to get a picture with the highlights NOT blown out to white (think of the sky) and shadows dark but able to see fine detail.
If someone else can offer more insight (and correct me if I’m wrong), that’d be great.
Hope this helps!
This is not at all what HDR video is. HDR for photgraphy (bracketing and combining) is a totally different animal.