Ancillary revenue is the revenue generated from activities or services provided by a company, apart from its primary products or services. Some common synonyms for ancillary revenue include additional income, supplementary income, incidental income, and secondary revenue. Other synonyms that more specifically refer to certain sources of ancillary revenue include cross-selling revenue, upselling revenue, and subscription revenue. In the airline industry, some synonyms for ancillary revenue include baggage fees, seat selection fees, and in-flight sales. Regardless of the industry, ancillary revenue streams are becoming more important for companies as they seek to diversify their revenue streams and increase overall profitability.