Definition - What does Viscosity mean?
Viscosity is defined as a fluid's resistance to flow. A fluid with a high viscosity does not flow very easily whereas a fluid with a low viscosity would readily flow when a force is exerted upon it.
Viscosity can also be defined as a fluid's "thickness" or its internal resistance to a shear stress. This resistance occurs due to the friction among the individual molecules in a fluid. The "thicker" the fluid, or the denser its molecular makeup, then the more friction there is to overcome when a shear stress is applied to the fluid.
Viscosity is an important variable to consider when selecting or mixing a coating for corrosion protection. Certain coatings are too viscous to be sprayed. Other coatings aren't viscous enough to create a thick enough coating. Multiple layers may be needed to remedy this particular problem. Materials that are too viscous may not coat evenly, which could result in earlier than expected coating deterioration.
Corrosionpedia explains Viscosity
The viscosity of liquid materials can vary when the temperature is changed. When temperature is increased, a liquid's viscosity generally decreases. An example of this would be caramel that is melted in a pan. At first it is very sticky and nearly impossible to stir, but after heat is applied the stirring becomes easier. This reduced viscosity occurs because as the temperature increases the molecules move around more. This movement spreads the molecules farther apart and reduces the forces of friction among themselves.