back pressure

noun

1. a resistant pressure exerted by liquid or gas against the forward motion or flow of an exhaust or pipe system: Careful control of backpressure ensures an even supply of oil from the well.

noun

1. engineering
   1. the pressure that opposes the motion of a piston on its exhaust stroke in an internal-combustion engine
   2. the exhaust pressure in external combustion engines
2. med the local pressure that builds up when fluid flow is obstructed in the cardiovascular or urinary systems

n.

1. Pressure exerted upstream in the circulation as a result of obstruction to forward flow, as when congestion in the pulmonary circulation results from failure of the left ventricle.