What does the term 'viscous' generally refer to in terms of material behavior?

The term 'viscous' primarily refers to a material's resistance to flow. In a viscous substance, the internal friction between its molecules hinders movement, making it flow less easily than a less viscous substance. For example, honey is more viscous than water, requiring more force to move or pour it.

This property is important in various fields, including fluid dynamics, engineering, and biological systems, as it affects how substances behave under stress, their movement within systems, and their interactions with other materials. Viscosity can be quantified and is a critical parameter in understanding the behavior of liquids and gases in motion, especially in applications like blood flow in the circulatory system or the behavior of industrial liquids.