Circuit: a closed loop that allows electricity to flow.
A common example of a circuit is a power cord. When you turn on an electrical device that plugs into the wall, you are closing a circuit. This circuit allows a current to flow from the power lines into the walls, through the outlet and the power cord to your device, and back through the cord and out again.
Electricity will remain in a circuit until the circuit is broken (such as when a device is unplugged or switched off) or until the electricity is given a path to the ground, called a short circuit.