Tensile yield stress is the amount of stress a material can withstand before it starts to deform plastically, meaning it will not return to its original shape after the stress is removed. It is a measure of the strength of a material and is typically determined through tensile testing, where a sample of the material is subjected to increasing amounts of stress until it reaches its yield point. The tensile yield stress is expressed in units of pressure, such as pounds per square inch (psi) or megapascals (MPa), and is an important parameter in the design and analysis of structural components and materials.