Under exposure
- An underexposed image is the sort of photograph that one might consider to be too dark.
Ref - https://photographylife.com/underexposure-and-overexposure-in-photography

Over exposure
- Overexposure is the complete opposite of the previously defined term. An image that is brighter than it should be can be considered overexposed. When too much light is allowed during exposure, the result is an overly bright photograph.
Ref - https://photographylife.com/underexposure-and-overexposure-in-photography

Correct Normal Exposure
- Correctly exposed image is the one that feels just bright or dark enough so that both the shadows and highlights are as they feel the most natural and comfortable to look at. Theoretically, such a photograph contains no lost highlights or shadows, meaning all the detail is clearly distinguishable and as close as possible to “real life”.
Ref - https://photographylife.com/underexposure-and-overexposure-in-photography

Bracketing / Autobracketing
- Autobracketing allows your camera to take multiple photos (say 3) in rapid sequence. Each one of those photos will be at a different shutter speed. If you are poking around your camera now, just like for the letters “BKT” for Bracket, and then maybe you can see how you can set it for three exposures at -2, 0, and +2. But more on this soon.
Ref - https://iso.500px.com/hdr-photography-tutorial/

HDR Photography (High Dynamic Range Photography)
- HDR is an acronym for High Dynamic Range. If you use some special HDR software, you can see all the light in the final photo that you can see when you are standing on the scene. Perhaps you’ve been in a beautiful spot and taken a photo and it comes out flat and disappointing. With HDR processing, there is no longer a need for that — now the final image can be as truly evocative as it was when you were there. The human eye can see so much more than a single shot from your camera! I say there is no need to accept the limitations of the camera. You can use the camera in a simple and innovative way to replicate what the eye can do. You’ll be using a combination of the camera and some software to achieve the final look. The human eye can see about 11 stops of light. A stop is a measurable amount of light. A camera can see about 3 stops of light. This means you’ll be setting up your camera to take multiple photos of a scene, all at different shutter speeds, so you get the full range of light. Don’t worry, it’s easy!
Ref - https://iso.500px.com/hdr-photography-tutorial/