Viscosity refers to a fluid's resistance to flow. Fluids with high viscosity, like honey, flow more slowly than low-viscosity fluids, like water.
Newtonian Fluid: A fluid whose viscosity remains constant, regardless of the forces acting upon it.
Non-Newtonian Fluid: A fluid whose viscosity changes depending on the force applied. Examples include ketchup or quicksand.
Shear Rate: This refers to how quickly a liquid’s particles move relative to each other. It can affect a liquid's apparent viscosity.