Which type of stress acts parallel to another but is not on the same plane?

Shear stress is a type of stress that occurs when forces are applied parallel to a material's surface, but not within the same plane. This is distinctive from other types of stress, as tensile and compressive stresses act along the same axis—either pulling apart or pushing together. Ultimate stress is more of a measure of maximum stress a material can endure before failure and does not describe the stress orientation.

In practical terms, shear stress is critical in situations like the analysis of beams under lateral loads or in mechanical connections, where components might experience sliding forces. Understanding shear stress is essential for assessing how materials will respond under different loading conditions, particularly when designing structures or mechanical systems.