Final answer:
User defined interfaces used for client data are called User interfaces, designed to enhance interaction with systems and data.
Step-by-step explanation:
User defined interfaces typically used for client data are called User interfaces. These interfaces are crafted to suit the specific needs and preferences of the client, facilitating easier interaction with data and systems. User interfaces (UI) can range from graphical user interfaces (GUIs) with buttons and images to command-line interfaces (CLIs) that operate through text-based input. The primary goal of a user interface is to make the user's interaction as simple and efficient as possible, where 'user' refers to the human who is interacting with the computer system or application.