What do you mean by upselling term?

Upselling is a selling technique where a seller introduces a more expensive, an upgrade, or add-on to a buyer to increase the average order value Upselling is a sales strategy that involves encouraging customers to buy a higher-end version of a product than what they originally intended to purchase. … Both upselling and cross-selling are methods of increasing sales to existing customers, but use slightly different approaches in doing so.