A more thorough explanation:

Term: In clientela
Definition: In ancient Rome, in clientela referred to the relationship between a client and a patron. A client was a person who received protection and support from a patron in exchange for loyalty and services. The patron was usually a wealthy and powerful person who provided the client with financial assistance, legal representation, and other benefits. The term in clientela was used to describe the dependence of the client on the patron and the obligations that came with this relationship.
Example: Marcus was a client of Gaius, a wealthy senator. Gaius provided Marcus with a place to live, food, and clothing. In return, Marcus had to be loyal to Gaius and perform various tasks for him, such as running errands and attending social events. Marcus was in clientela to Gaius, which meant that he was dependent on him for his livelihood and had to follow his orders.
Example: Julia was a patron of several clients who were artists and writers. She provided them with financial support and helped them publish their works. In return, the clients dedicated their works to her and praised her in their writings. Julia's clients were in clientela to her, which meant that they owed her loyalty and had to promote her interests.