A non-newtonian fluid is a thixotropic fluid which changes its viscosity when the shearing forces it is exposed to change. Other flow properties may also be affected. Most commonly viscosity of such fluids is not independent of the shear rate or the shear rate history. Examples of such fluids are blood, quicksand and certain components of cement. Many lubricants, ketchup, certain forms of dough and pudding also have this property.
The other kind of fluids that do not show this behaviour are called Newtonian fluids.