HDR
An
HDR image is commonly made by taking three photos of the same scene, each at different shutter speeds. The result is a bright, medium, and dark
photo, based on the amount of light that got through the lens. A software process then combines all the photos to bring details to the shadows and highlights both.
So a 3-shot HDR takes 3 images of different "exposure" and then we combine them into a single HDR image. 5-shot simply uses more shots and thus a wider range of exposures.
Newer DJI aircraft offer you the option of HDR inside the camera. The camera still shoots 3 images but they are combined inside the system and a single HDR processed image it saved on your SD card. I personally prefer to do the combining so I can TWEAK the photos as I'm going to give the best possible (IMHO) finished product.
Hope that helps some