An aspirator is a type of ejector-jet pump, that produces vacuum by means of the Venturi effect.

In an aspirator, fluid (liquid or gaseous) flows through a tube which narrows then expands in cross-sectional area, and thus volume. When the tube narrows the fluid's pressure decreases. In this narrow area the fluid velocity must increase to conserve mass continuity. Where the tube narrows a vacuum is drawn because of the Venturi effect.