Fluids for which the shearing stress is linearly related to the rate of shearing strain are designated as Newtonian Fluids.
Newtonian materials are referred to as true liquids since their viscosity or consistency is not affected by shear such as agitation or pumping at a constant temperature. Fortunately most common fluids, both liquids and gases, are Newtonian. Water and oils are examples of Newtonian liquids.