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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. The VBLANK signal is generated by S-PPU2 (pin 26), which is fed into the S-CPU through pin 44.
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. The HBLANK signal is also generated by S-PPU2 (pin 25), which is fed into the S-CPU through pin 43.
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.