What is the term for the resistance encountered when a liquid or gas flows?

The term for the resistance encountered when a liquid or gas flows is referred to as viscosity. Viscosity is a measure of a fluid's thickness or internal friction, determining how easily it flows. A fluid with high viscosity flows more slowly and with more resistance, while a fluid with low viscosity flows easily.

Understanding viscosity is crucial in various applications, such as engineering, fluid dynamics, and even in everyday products like honey or motor oil, where different viscosities significantly impact performance. The concept of viscosity not only pertains to the resistance to flow but also influences how fluids behave under different conditions, making it an essential factor in the study of fluid mechanics and aerodynamics.