A low-cost carrier or low-cost airline (also known as a no-frills, discount or budget carrier or airline, or LCC) is an airline that generally has lower fares and fewer comforts. To make up for revenue lost in decreased ticket prices, the airline may charge for extras like food, priority boarding, seat allocating, and baggage etc. Currently the world's largest low-cost carrier is Southwest Airlines, which operates in the United States and 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.

In due course, some airlines have actively sought to market and advertise themselves as low-cost, budget, or discount airlines while maintaining products usually associated with traditional mainline carrier's services which often result in increased operational complexity. Among these products, which tend to increase complexity and reduce efficiency, are: preferred or assigned seating, catering other items rather than basic beverages, 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" has been designated to differentiate some low-cost carriers, particularly in North America where traditional airlines increasingly offer a similar service model to low-cost carriers.