aperture

A small or narrow opening, gap, slit, or hole.

an aperture in a wall

Were the larynx of the little creature like that of the parent, the milk might—probably would—enter the windpipe and cause suffocation : but the fœtal larynx is cone-shaped, with the opening at the apex, which projects, as in the whale-tribe, into the back aperture of the nostrils, where it is closely embraced by muscles of the ‘soft palate.’

A hole which restricts the diameter of the lightpath through one plane in an optical system.

A hole which restricts the diameter of the lightpath through one plane in an optical system.

This telescope has a 100 cm aperture.

The (typically) large-diameter antenna used for receiving and transmitting radio frequency energy containing the data used in communication satellites, especially in the geostationary belt. For a comsat, this is typically a large reflective

The maximum angle between the two generatrices.

If the generatrix makes an angle θ to the axis, then the aperture is 2θ.