Consider the circuit shown.
In a circuit with a light emitting diode and resistor R2 you add the p-gate thyristor C 106D. The cathode is connected to the negative terminal of the battery, the anode through the LED to the positive terminal.
When connecting the battery, the light emitting diode LED1 remains dark. The thyristor blocks any current between the anode and the cathode. It is said that the thyristor is in its OFF state.
However, a thyristor has a third connector, the gate...
In the next experiment you put the thyristor in its ON state.