Plain English Meaning
A small hole in a line, made on purpose to slow down how fast fluid or air can pass through it. It acts like a built-in throttle, keeping things from moving too quickly.
Full Definition
A small, deliberately narrowed opening placed in a fluid or air line to limit the rate of flow through it. In aircraft systems, restricted orifices are used to slow the movement of hydraulic fluid, pneumatic air, or oil so that components extend, retract, or actuate at a controlled, predictable speed.
Context Anchor
Seen in the principle of operation for the vertical speed indicator in the pitot-static instrument system.