Abstraction - The act of considering something as general quality or characteristic, apart from concrete realities, specific objects or actual instances.
Abstract photography/art allows people to interprate the image/drawing in the way you see it and can be many different things with no right or wrong answer. The image is usually not a literal view on itself, however with a slight twist to point it onto a different view on something else. Abstract pictures help people to not just look at pictures, but look into them and try to make sense of something that may not anything in particular.
Above and below are some examples of abstract photography and I like them because they draw you into the image so you look at the detail totry and make sense of them even if they don't.