| aperture | |
| 1. n. An opening, gap, or hole, usually small and narrow | |
| an aperture in a wall | |
| 2. n. (optics) Something which restricts the diameter of the light path through one plane in an optical system. | |
| 3. n. (astronomy, photography) 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 | |
| This telescope has a 100cm aperture. | |
| 4. n. (spaceflight, communications) The (typically) large-diameter antenna used for receiving and transmitting radio frequency energy containing the data used in communication satellites, especially in the | |
| 5. n. (mathematics, rare, of a right circular cone) The maximum angle between the two generatrices. | |
| If the generatrix makes an angle θ to the axis, then the aperture is 2θ. | |
