Question

What is an open circuit

Answer 1

Literally, A circuit which is open is called as Open circuit.
Now, why do we need terms like open or closed circuit, this is because,

if there is any component not properly conneted, then the circuit may not function properly, or no current may flow through it, and no current flows through a circuit which has no battery, or if it is broken or OPEN.
so it is called an open circuit.

Definition: An electric circuit in which the normal path of current has been interrupted, by the disconnection of one part of its conducting pathway from another