A vertical blank interrupt (or VBI) is a hardware feature found in some legacy computer systems that generate a video signal.
The interrupt service routine can then modify data in the video display memory while it is not being read to avoid screen tearing effects.
[1] This was particularly useful in simple home computers and video game consoles that relied upon a central microprocessor to generate text or graphic displays.
More advanced home computers featuring hardware sprites often supported the more flexible horizontal blank interrupt instead in order to allow them to be multiplexed.
It can also be used to implement a basic form of multitasking as well as a buffered graphics screen via page flipping, if hardware permits.