Steady and unsteady flow

Steady flow-

When fluid properties of the system flowing through a control volume don't change concerning time then it is known as steady flow.
Or,
In steady flow Fluid, velocity will be constant at the different points at the same time.

Unsteady flow-

When fluid properties of the system(e.g.- pressure, temperature, density) flowing through a control volume change with time then it is known as unsteady flow.

Or,

In unsteady fluid flow, velocity may increase or decrease at different points at the same time