Short answer: Dynamic range in photography is the difference between the lightest parts of an image and the darkest parts. In photography, this is usually measured in f-stops.
The Subjects Dynamic Range, Your Cameras, and Your Eye’s
In photography there are three ways in which dynamic range is usually covered. The main one is your camera’s dynamic range. A good camera should be capable of capturing 12-15 f-stops of data within a single image. Resource: How-To Geek
The human eye has a static dynamic range of about 6.5 f-stops which adjusts to match the scene within a luminance range of about 46.5 f-stops. Resource: Wikipedia. However, this is hotly debated online with many different numbers being used and is enough for it’s own post. See some of the debate on Digital Photography Review.
Then there’s the dynamic range in the scene you are capturing. If the dynamic range in the scene is greater than the dynamic range of your camera, light and dark shades will become crushed into one which is called clipping.
Clipping happens when there are subtle differences in light and dark shades that are being lost because they are outside of the dynamic range the camera is capable of capturing all at once. In the above photo the sky is a uniform white when there were subtle details in the clouds on the day. Everything that is near to white is being counted as white and the detail is not present in the image. This is clipping and in the above example this creates a blown out sky which is a common effect of clipping.
How your camera will typically set it’s range is by picking out the middle grey of the scene and then allowing the dynamic range to extend equally from that point. So if your scene has more range than your camera is capable of you will get dark greys coming out as blacks and near-whites as whites as well.
You can get a good sense of this by looking at your camera’s histogram.
Your camera’s histogram shows you the distribution of light in a captured image and live in your scene. If the values in the graph are all on the right then this means the scene is bright and is an indication that you might be missing information in the highlights. If your camera gives you a live histogram of your scene then you can adjust your exposure, for example by using a faster shutter speed, and see if there are details you were missing.
Likewise, if all your values are to the left then this shows this is a dark scene you are capturing. Here’s a good video from Matt Granger on YouTube who discusses some of the finer points of using histograms:
Shooting in RAW
To increase the dynamic range available in your images then you should shoot in RAW. A RAW image is an unprocessed image and so contains more information. You will have access to greater shadow and highlight details when editing a RAW image than an image format like a JPEG.
What is HDR?
HDR stands for High Dynamic Range. This is a technique where multiple images are taken of a scene at different exposures and then combined to create an overall image which displays a greater dynamic range than your camera is capable of taking in one shot.
In the above image you can see that there are details in the clouds which are subtle shades of grey and the grass is bright, almost luminescent, as well. If you were to take this as one image you might find that having details in the clouds means sacrificing brightness in the grass and poppies. Or if you focus on having the grass bright then the sky will be blown out.
A great video from Tony & Chelsea Northup on YouTube: