We can define it very easily, it is the amount of angle that lens can capture. How I said, very simple. But how to use it and how it can help you? With wider lenses you can get a lot of stuff in the photo. These lenses are great for landscapes, journalists etc. Sometimes you have to narrow the angle of view to get less objects in photo. Here is a short video done by Mark Wallace and Adorama TV.
There is another reason why you should know something more about the angle of view. Using wide and ultra-wide lenses you can pick one subject in the foreground and make him stand out in comparison with background. Cameras don’t see in 3D space, so closer objects are bigger and objects furhter away are smaller. This proportion is increased when you use wide lenses.
On oposite site, sometimes you need that flat look and using wide lens won’t work. A perfect example for this are portraits. You can break the rule, it isn’t carved in stone, but you have to know how to use it otherwise you won’t have good results.
Here are some examples of using the angle of view. First I was wide and wanted to capture the whole scene. But after some time I’ve realized, the top isn’t so good. I just zoomed in and excluded it from the picture.