The light coming into your camera is controlled by the iris
The aperture size regulates the amount of light that you allow into your camera while taking a picture. However, it is the ‘Iris Diaphragm’ mechanism that controls the aperture size. It is a sophisticated mechanism in today’s cameras. In former times the diaphragm was a component of the lens in its own right. Today the iris and the diaphragm are one mechanism which together control aperture size .
The new entry in the Photographic Glossary: Diaphragm; Iris Diaphragm; Iris