What is a closed and open circuit ?

Closed circuit:

A closed or close circuit is one in which, the switch is CLOSED. This allows for the flow of current in the circuit. Current flows from the battery in the circuit and through the load in the circuit.

Open circuit:

An open circuit is one in which the circuit is OPEN. Since the switch is open, the circuit is broken and hence the current from the battery or cell cannot flow.

In the circuit and there is no voltage drop across the load.