Wikipedia
Cross-selling is the action or practice of selling an additional product or service to an existing customer. In practice, businesses define cross-selling in many different ways. Elements that might influence the definition might include the size of the business, the industry sector it operates within and the financial motivations of those required to define the term.
The objectives of cross-selling can be either to increase the income derived from the client or to protect the relationship with the client or clients. The approach to the process of cross-selling can be varied.
Unlike the acquiring of new business, cross-selling involves an element of risk that existing relationships with the client could be disrupted. For that reason, it is important to ensure that the additional product or service being sold to the client or clients enhances the value the client or clients get from the organization.
In practice, large businesses usually combine cross-selling and up-selling techniques to increase revenue.