The Venturi effect is the reduction in fluid pressure that results when a moving fluid speeds up as it flows from one section of a pipe to a smaller section. The Venturi effect is named after its discoverer, the Italian physicist Giovanni Battista Venturi, and was first published in 1797.
The Venturi effect describes how the velocity of a fluid increases as the cross section of the container it flows in decreases (like when flowing through a funnel).
Everyday products such as the choke on an engine or the air pump on a fish tank use the Venturi Effect. The Venturi Effect goes against the natural assumption that pushing fluid through a restricted pipe increases pressure when in reality the increase in velocity leads to a reduction in pressure.