In fluid dynamics, a synthetic jet flow — is a type of jet flow, which is made up of the surrounding  fluid.   Synthetic jets are produced by periodic ejection and suction of fluid from an opening. This oscillatory motion may be driven by a piston or diaphragm inside a cavity among other ways.
A jet flow is a fluid flow in which a stream of one fluid mixes with a surrounding medium. An example is a water jet that forms when you put your thumb over the end of a hose. The water mixes with air to form a jet.  If you increase the flow of water or move your thumb to change the diameter of the exit, the jet will change dramatically.
Jet flows vary depending on velocity and diameter of the flow and the density and viscosity of the fluid (Reynolds number and Mach number). When the velocities in the jet are greater than the speed of sound, important qualitative changes in the flow occur. One such change is that shock waves form.
A synthetic jet flow was so named by Ari Glezer since  the flow is "synthesized" from the surrounding or ambient fluid.  Producing a convectional jet requires an external source of fluid, such as piped-in compressed air or plumbing for water.