Throttling is the process of restricting the flow of a liquid or a gas in a pipeline.  Throttling is done using a valve, a porous plug or an orifice.  A flexible hose can be throttled by pressing it.

Throttling is used to limit the flow in industrial systems.  For example, the flow of air or fuel to an engine can be throttled.  This would vary the power output of the engine.  The speed control in a vehicle is called the throttling system.

The throttling process can result in a drop in temperature due to the Joule Thomson effect.