Therefore a vertical blanking pulse is generated for every frame.

This vertical blanking pulse is not visible on the display, nor is any pixel sent.

Most consumer VCRs use the known black level of the vertical blanking pulse to set their recording levels.

Most VCR circuits use the amplitude of the vertical blanking pulse to operate the AGC.

The portion of a composite picture signal that lies between the leading edge of the horizontal blanking pulse and the leading edge of the corresponding sync pulse.

So, the NTSC signal includes a short sample of this reference signal, known as the colorburst, located on the 'back porch' of each horizontal line (the time between the end of the horizontal synchronization pulse and the end of the blanking pulse.)