That may sound like a strange question at first. However, the terms ‘add-on’ and ‘ancillary’ can mean different things across industries. In the airline industry, ancillary is a commonly used term to describe products and services that are purchased by customers that are not included in the basic ticket price, e.g. bags, seats, cars, hotels, insurance, parking, transfers etc. In retail or insurance they refer to additional products purchased by the customers as add-ons, upsell or cross sell products. Throughout this site we use the term add-on and what our definition of an ‘add-on’ is any additional product or service a customer purchases that is added to a core product purchase.