A small or narrow opening, gap, slit, or hole.
The diameter of such a hole which restricts the width of the lightpath through the whole system. For a telescope, this is the diameter of the objective lens.
A hole which restricts the diameter of the lightpath through one plane in an optical system.
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.
The maximum angle between the two generatrices.
Any small opening resembling the hole for a key in shape or function.
A mortise for a key or cotter.
A gravitational keyhole.
A hole or excavation in beams intended to be joined together, to receive the key that fastens them.
A transient column of vapor or plasma formed when using high energy beams, such as lasers, for welding or cutting.
The free-throw lane together with the circle surrounding the free-throw line; key.
The hole in a lock where the key is inserted and turns.
A circle cut out of a garment as a decorative effect, typically at the front or back neckline of a dress.
A welding method in which a hole forms in the surface immediately ahead of the puddle in the direction of welding. The hole is filled as the weld progresses.
To strike a target after wobbling in flight so that the long axis of the bullet does not follow the line of flight, typically due to insufficient spin resulting from the rifling in the barrel.