The representation of a digital image as points, lines and other geometric entities.  All computer-aided design (CAD), drawing and diagramming programs create vector images (see 
graphics formats).
Vector graphics and "bitmapped graphics" are the two fundamental structures for digital images (see 
graphics for basic concepts).  However, vector images are very space efficient compared to bitmapped images, and they maintain all their detail when zoomed in and out because they are rendered in real time.  For an example of vector coding, see 
SVG.