What is the resistance of a gas or liquid to flow known as?

Viscosity refers to the resistance of a gas or liquid to flow. It is a measure of how easily a fluid moves; higher viscosity means a thicker fluid that flows more slowly, while lower viscosity indicates a thinner fluid that flows more easily. This property plays a crucial role in various natural and industrial processes, such as the movement of oil through pipelines or the behavior of magma in volcanoes.

Density relates to the mass of a substance per unit volume and is not specific to flow resistance. Conductivity involves how well a material can conduct electricity or heat, and reactivity refers to how readily a substance undergoes a chemical reaction. Thus, these terms do not accurately describe the flow characteristics of fluids.