The Plasticity Index (PI) is a measure used in soil science to determine the plasticity of a soil sample. It is calculated by subtracting the soil's Plastic Limit from its Liquid Limit. A higher PI indicates that the soil can undergo more deformation without cracking or breaking, which is important for construction and engineering projects. Understanding the Plasticity Index helps engineers assess soil behavior under different moisture conditions. Soils with a high PI can be more challenging to work with, as they may expand when wet and shrink when dry. This information is crucial for designing stable foundations and structures.