A simple model of a circuit?

An electric circuit is a closed loop that allows a flow of electrons to begin from a source of the electrons and return to the same source.

Some of the energy carried by the current from the source may or may not be released to perform useful work.

Because of the resistance of the materials in the circuit, some of the energy carried by the current is always lost as heat emitted from the circuit into the surrounding environment.

The flow of electrons around the closed loop is called an electric current.

The source of the electrons must be a chemical battery or a mechanical generator which produces a potential difference, also known as a voltage.