The voltage at which the insulator punctures is called the puncture voltage. When the puncture voltage is exceeded, the insulator is permanently damaged as the current flows through the inside of the insulator.
The creepage distance refers to the distance over the surface between the conductor and the ground. The creepage distance in insulators is increased by corrugating the body. The creepage distance depends on the voltage. Higher voltages will require higher creepage distances.
The Flashover distance is the minimum distance below which a flash over can occur.
The voltage above which a Flashover can occur is called the Flashover voltage.