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Blanking
From SnesLab
Blanking is the cutting of electronic current from the cathode to the screen in a CRT television while it is switched on.
Vertical blanking occurs when the electron beam reaches the bottom-right of the screen and needs to be reset to the top-left again.
Horizontal blanking occurs when the electron beam reaches the end of a scanline and needs to be reset to the beginning of the next scanline.
Forced blanking occurs when the PPU nearly switched off, so it is generating black, but this is not part of the TV's sync pulse.