What is the term for the resistance offered to a layer of fluids when it moves over another layer?

The term for the resistance offered to a layer of fluids when it moves over another layer is viscosity. Viscosity is a measure of a fluid's resistance to deformation and flow. It describes how thick or sticky a fluid is and indicates how easily it can flow. For instance, honey has a higher viscosity than water, meaning it flows more slowly and offers greater resistance when layers of the fluid try to slide past one another.

Understanding viscosity is crucial in various civil engineering applications, particularly in hydraulics, where fluid behavior affects designs for pipes, channels, and the behavior of fluids in different conditions. The other terms mentioned do not pertain directly to the concept of resistance between moving fluid layers. Density refers to mass per unit volume, pressure pertains to the force exerted by a fluid per unit area, and specific gravity is the ratio of a fluid's density to the density of a reference substance (usually water) but does not describe fluid resistance directly.