aperture

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

2. (optics) A hole which restricts the diameter of the lightpath through one plane in an optical system.Examples: "This telescope has a 100 cm aperture."

3. (space flight, communication) 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.

4. (mathematics, rare, of a right circular cone) The maximum angle between the two generatrices.Examples: "If the generatrix makes an angle θ to the axis, then the aperture is 2θ."rare