If a bulb, wire, and cell are put together in the correct way, the bulb will light. Together they form a system. A system is a group of things that work together. The bulb, wire, and cell work as an electrical system. The system uses electric energy to light the bulb.
Electricity is a form of energy that travels in a circuit.
A circuit is the path through which electricity flows. A circuit is like a train track. Just as the track must be complete before a train can travel on it, a circuit must be complete for electricity to flow. A complete circuit is called closed circuit. A closed circuit has no gaps.