Permeability is a measure of how easily fluids, like water or air, can pass through a material. It is an important property in fields such as geology, engineering, and environmental science. For example, soil with high permeability allows water to flow through it quickly, while clay has low permeability, making it harder for water to move. In construction, understanding permeability helps engineers choose the right materials for foundations and drainage systems. High permeability materials can help manage water flow, while low permeability materials can prevent unwanted water infiltration, protecting structures from damage.