Song, LLC, was a low-cost air service within an airline brand owned and operated by Delta Air Lines from 2003 to 2006. All Song flights were operated by Delta. Song's main focus was on leisure traffic between the Northeastern United States and Florida, a market where it competed with JetBlue Airways. It also operated flights between Florida and the West Coast, and from the Northeast to the West Coast.

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.