A low-cost carrier or low-cost airline (occasionally referred to as no-frills, budget or discount carrier or airline, and abbreviated as LCC) is an airline that is operated with an especially high emphasis on minimizing operating costs and without some of the traditional services and amenities provided in the fare, resulting in lower fares and fewer comforts. 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.

The term originated within the airline industry referring to airlines with a lower operating cost structure than their competitors. While the term is often applied to any carrier with low ticket prices and limited services, regardless of their operating models, low-cost carriers should not be confused with regional airlines that operate short flights without service, or with full-service airlines offering some reduced fares.

Some airlines advertise themselves as low-cost while maintaining products usually associated with traditional mainline carrier's services. These products include preferred or assigned seating, catering, differentiated premium cabins, satellite or ground-based Wi-Fi internet, and in-flight audio and video entertainment. More recently, the term "ultra low-cost carrier" (ULCC) has been used, particularly in North America and Europe to refer to carriers that do not provide these services and amenities.