What is it?

Vector graphics are images, usually 3D, that are made up of lines called vectors that form an outline of the objects in the image. Many video games were made with vector graphics, because they are fairly easy to make and render at a playable framerate, even on the computers of the 1970s and 1980s. Vector graphics usually use two colors, one for the background and one for the objects. An advantage that vector graphics have over images made with pixels is that you can zoom in to any magnification and it will never get pixelated.

This is what a vector game looks like: