"The tourism services produced by companies in the tourism industry are not always offered directly to the end consumer, the traveler. Package tours or partial tourism services are often sold via an "intermediary". The best-known form of this intermediary or distribution channel is travel agencies. They sell the respective tourism service to the end consumer/tourist on behalf of the producer/manufacturer. In tourism terminology, this is referred to as an "intermediary service" and the corresponding companies as travel agents. - In addition, other institutions also broker tourism services, such as travel clubs and associations, tourist offices, travel agencies of companies, etc.".
Source: Freyer, W. (2001). Tourismus Einführung in die Fremdenverkehrsökonomie (7th edition). Munich: Oldenbourg Wissenschaftsverlag