Non-Newtonian fluid

In rheology, the science of fluids, a non-Newtonian fluid is one whose viscosity changes with the applied shear force.

Types of non-Newtonian fluid include:

rheopectic (viscosity increases with increasing force, as in some lubricants)
thixotropic (viscosity decreases with increasing force; e.g. non-drip paints; tomato ketchup)