circuit science definition

1. A closed path through which an electric current flows or may flow.
   ♦ Circuits in which a power source is connected to two or more components (such as light bulbs, or logic gates in a computer circuit), one after the other, are called series circuits. If the circuit is broken, none of the components receives a current. Circuits in which a power source is directly connected to two or more components are called parallel circuits. If a break occurs in the circuit, only the component along whose path the break occurs stops receiving a current.
2. A system of electrically connected parts or devices.

circuit

Bulbs in a simple circuit (top) and parallel circuit (bottom left) emit bright light since each is directly connected in its own circuit to a power source. Bulbs in a series circuit (bottom right) emit dim light since each consumes a portion of the battery's power coming through a single circuit.