The pressure within a system caused by fluid friction or an induced resistance to flow through the system. Most process facilities require a minimum system pressure to operate efficiently. The necessary back-pressure is often created and controlled by a valve that is set to operate under the desired range of conditions.

The resistance that reduces forward flow in an extruder.

The amount of air pressure that a player feels when he or she breathes into a flute. This is typically a matter of flute construction, but could possibly be due to obstructions in the flue or slow air [..]

In a fuel kiln, the internal pressure resulting from proper balance of combustion pressure and damper setting, resulting in more economical and efficient heatwork. Source: Clay: A Studio Handbook