aperture

Definitions

• An opening, gap, or hole, usually small and narrow
• (optics) Something which restricts the diameter of the light path through one plane in an optical system.
• (astronomy) The diameter of the aperture (in the sense above) which restricts the width of the light path through the whole system. For a telescope, this is the diameter of the objective lens.
• (spaceflight) 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 dish antenna; sometimes called an array.
• (mathematics) The maximum angle between the two generatrices.