Compare with Newtonian fluid. A fluid whose viscosity changes when the gradient in flow speed changes. Colloidal suspensions and polymer solutions like ketchup and starch/water paste are non-Newtonian fluids.
a fluid is said to be Non-Newtonian, if Viscosity increases with shear rate (Shear – Thickening) or Viscosity decreases with shear rate (Shear – Thinning).
A non-Newtonian fluid is a fluid in which the viscosity changes with the applied strain rate. As a result, non-Newtonian fluids may not have a well-defined viscosity.