Viscosity is a physical property of liquids and gases that describes their internal friction or resistance to flow and deformation. It is a measure of how viscous or thin a substance is. A single molecule experiences a frictional force in a thick liquid or gas as it moves through the sense.
This internal friction between the individual molecules affects the flow behaviour of the liquid or gas. A fluid with high viscosity is thick and resists flow, so it moves more slowly. Honey or syrup are examples of liquids with high viscosity. On the other hand, a drink with low viscosity has a thin-bodied nature and flows more easily and quickly. Water is an example of a liquid with low viscosity.