**Explanation:**

An open circuit refers to a circuit in which there is a break or interruption in the path of current flow. In other words, it is a circuit where there is no complete conducting path for the current to flow.

When a circuit is open, it means that the two terminals of a device or component are not connected to each other. This can occur due to a variety of reasons such as a switch being turned off, a wire being disconnected, or a component being faulty.

When there is an open circuit, the flow of current is interrupted and cannot complete the loop. As a result, no current flows through the circuit. This is why the correct answer is option 'D' - no current flows through the cell.

**Example:**

Let's consider a simple circuit consisting of a battery and a resistor. When the circuit is closed, i.e., there is a complete conducting path, the current can flow from the battery through the resistor and back to the battery. This is called a closed circuit.

However, if we disconnect one end of the resistor from the battery, we create an open circuit. In this case, there is no complete path for the current to flow. Even though the battery might have the potential to drive current, it cannot do so because there is no closed loop.

**Effects of an Open Circuit:**

- No current flows through the circuit.
- The flow of electrons is interrupted.
- The components in the circuit do not receive any power or voltage.
- Devices such as lights, motors, or other electrical appliances connected to the circuit will not function.

**Conclusion:**

In summary, an open circuit refers to a circuit where there is a break or interruption in the path of current flow. This means that no current flows through the circuit, and the components connected to the circuit do not receive any power or voltage.