A path between two points over which an electrical signal can pass. In telecommunications, a circuit is a path over which voice, data, or other analog or digital signals can pass.
A physical circuit is a collection of wires or cables that are connected with switches or other devices; it can be thought of as a straight line between the two endpoints.
Balanced circuits typically support higher data transmission rates because they are less susceptible to noise caused by electromagnetic interference (EMI) than unbalanced circuits.
A typical serial interface such as RS-232 includes specifications for a number of different types of circuits, including data circuits, control circuits, timing circuits, secondary circuits, and ground connections.