The memory in a computer's graphics adaptor, used to store the image displayed on a bitmap display. Often this is built using VRAM chips. There is normally a simple correspondence between groups of bits in video memory and the dots or "pixels" on the screen, such that writing to a given group of bits will alter the appearance of a single dot. If each pixel corresponds to eight bits then it can have any of 256 colours (or shades of grey on a monochrome display).
The video display electronics is responsible for reading the data from video memory and converting it into the necessary signals to drive the display. Often this includes a colour palette which converts pixel values into RGB triplets.