Aperture: an opening. from the Latin apere, to open. The term has the following specific meanings.

• Aperture in photography defines the size of the opening in the lens.
• Aperture is the diameter of the objective lens or primary mirror in a telescope.
• Synthetic aperture, a method in radioastronomy and radar measurements.
• Aperture is a physical parameter of an antenna.
• Aperture is the opening in the shell of a gastropod (mollusc).
• Aperture grille is a prominent cathode ray tube display technology.
• numerical aperture, a parameter of optical fibers and microscopy.