Pounds per Square Inch (PSI) is a unit of pressure that measures the force applied to a specific area. It indicates how much weight is exerted on one square inch of surface. For example, if a tire is inflated to 30 PSI, it means that there is a force of 30 pounds pressing on each square inch of the tire's surface. PSI is commonly used in various applications, including measuring tire pressure, hydraulic systems, and air compressors. Understanding PSI is essential for ensuring safety and efficiency in equipment like automobiles and industrial machinery. Proper pressure levels can enhance performance and prevent damage.