**1. n. [Drilling Fluids]**

A property of fluids and slurries that indicates their resistance to flow, defined as the ratio of shear stress to shear rate. Viscosity can be expressed mathematically as follows:
^{2}. Because one poise represents a high viscosity, 1/100 poise, or one centipoise (cp), is used for mud measurements. One centipoise equals one millipascal-second. Viscosity must have a stated or an understood shear rate in order to be meaningful. Measurement temperature also must be stated or understood.

**See:**
bentonite,
Bingham plastic model,
breaker,
Brookfield viscometer,
capillary tube viscometer,
carboxymethylcellulose,
centipoise,
derrickman,
direct-indicating viscometer,
funnel viscosity,
gel strength,
gyp mud,
Herschel-Bulkley fluid,
high-pressure, high-temperature viscometer,
Marsh funnel,
mud additive,
Newtonian fluid,
non-Newtonian fluid,
pill,
plastic fluid,
power-law fluid,
pseudoplastic,
PVT,
rheological property,
rheology,
shear rate,
shear stress,
VG meter,
yield

Viscosity.