What is any device called in which an electrical current flows and which changes this electrical energy into a more useful form?

The term used to describe any device through which an electrical current flows and converts electrical energy into a more useful form is "Load." Loads can take various forms, such as resistors, motors, or any other component that consumes electrical energy and transforms it into other types of energy such as light, heat, or mechanical energy.

In a circuit, the load is essential because it is the part of the system that does the work. For example, in a light bulb, electrical energy is transformed into light and heat; in an electric motor, electrical energy is converted into mechanical movement. This transformation is critical in utilizing electrical energy effectively, as it serves the purpose of providing a particular function that the circuit is designed to achieve.

Sources, on the other hand, provide electrical energy, switches control the flow of electrical current, and wires are the conduits through which current travels. While these components are integral to a circuit's operation, they do not fulfill the role of changing electrical energy into another form, which is the key function of a load.