**1. n. [Geology, Geophysics, Formation Evaluation]**

A measure of a material’s strength. The unconfined compressive strength (UCS) is the maximum axial compressive stress that a right-cylindrical sample of material can withstand under unconfined conditions—the confining stress is zero. It is also known as the *uniaxial compressive strength* of a material because the application of compressive stress is only along one axis—the longitudinal axis—of the sample.

**Alternate Form:**
unconfined compressive strength,
uniaxial compressive strength

Unconfined compression test.