What is long exposure photography?
Typically, long exposure usually refers to any photography that requires a tripod. There will always be places that are too dark and in order to get a good image you will have to increase ISO. Increasing your ISO introduce noise . This is when you should put your camera on a tripod. When you do that, you are starting to do long exposures.
Typically, you would do long exposures for night photography or if you are using special filters like ND filters that block many stops of light which will allow you to keep the shutter open for a long time.