Understanding exposure
Theory and Practice of Photography
Aperture:
Aperture is the setting of the iris of the camera lens. Just as your pupils in your eyes expand and contract to let in more or less light, you can do the same with your camera by setting the Aperture.
The Aperture measurement is called F-stop. The higher the F-stop number, the smaller the iris is set in your camera.
The trade-off: Each concept of photography seems to have a trade-off that prevents you from wanting to use it all the time.