1. n. 
The mass per unit volume of a drilling fluid, synonymous with mud density. Weight is reported in
Mud weight controls hydrostatic pressure in a wellbore and prevents unwanted flow into the well. The weight of the mud also prevents collapse of casing and the openhole. Excessive mud weight can cause lost circulation by propagating, and then filling, fractures in the rock. Mud weight (density) test procedures using a mud balance have been standardized and published by the API.
Synonyms: mud density
See: bland coring fluid, calcium bromide, cesium acetate, cesium formate, equivalent circulating density, formate, gunning the pits, high-gravity solids, kill-weight fluid, kilogram per cubic meter, mud, mud balance, mud program, pressurized mud balance, PVT, sag, slug, weighting material