UPDATED – One of the general property of the liquids is their resistance to change a form. This resistance is called viscosity and can be expressed as a resistance to flow. In case of liquids, the viscosity can be simply expressed as “thickness”. For example, water is “thin” with low viscosity, while honey is “thick” having a higher viscosity (see example on right). More technically speaking, viscosity is classically defined as the tangential force per unit area necessary to maintain unit relative velocity between two parallel plates in a liquid unit distance apart.