Pin 4 is called the RESET PIN. It is called an ACTIVE LOW pin. When pin 4 is HIGH, the chip operates normally. When pin 4 is taken LOW, the output of the chip is INHIBITED - it remains LOW. Pin 7 is also taken low and the chip is prevented from oscillating.
Mouseover the following animation to see the action of pin 4:
Mouseover the following animation to see the action of pin 4:
Mouse-over to INHIBIT the 555