1. The problem asks for the meaning of the abbreviation "PSI". 2. PSI commonly stands for "Pounds per Square Inch" in contexts such as pressure measurement. 3. It can also mean "Population Services International," "Python Software Index," or "Psionics" depending on the context. 4. Since this is not a math problem, but a terminology query, the answer must be understood in its specific field. Final answer: PSI typically means "Pounds per Square Inch."