Pacific Southwest Airlines (PSA) was a low-cost US airline headquartered in San Diego, California, that operated from 1949 to 1988. It was the first substantial scheduled discount airline. PSA called itself "The World's Friendliest Airline" and painted a smile on the nose of its airplanes, the PSA Grinningbirds. The Los Angeles Times called PSA "practically the unofficial flag carrier airline of California for almost forty years."

A low-cost carrier (LCC) or low-cost airline, also called no-frills, budget or discount carrier or airline, is an airline that is operated with an emphasis on minimizing operating costs. It sacrifices certain traditional airline luxuries, for cheaper fares. To make up for revenue lost in decreased ticket prices, the airline may charge extra fees such as for carry-on baggage. As of April 2020, the world's largest low-cost carrier is Southwest Airlines, which operates primarily in the United States, as well as in some surrounding areas.