Aperture is a topic that is related to optics. Aperture is simply a hole through which the light enters a chamber. This opening or a hole is widely used in cameras and other optical instruments such as a light microscope. For instance, the aperture opening in a camera or a microscope affects the amount of light entering the chamber and hence it changes the texture of the final image.
The aperture size along with the focal length, change the cone angle and the amount of rays that come to focus in image plane. Aperture is considered as one of the three pillars in photography.