The viscosity of a fluid is an important property in the analysis of liquid behavior and fluid motion near solid boundaries.
The viscosity is the fluid resistance to shear or flow and is a measure of the adhesive/cohesive of frictional fluid property. The resistance is caused by intermolecular friction exerted when layers of fluids attempt to slide by one another.
Viscosity is a measure of a fluid's resistance to flow.
The knowledge of viscosity is needed for proper design of required temperatures for storage, pumping or injection of fluids.