1.5.3. What Vector Graphics are

Definition

Vector graphics are images which are represented by the use of geometrical primitives such as points, lines, curves, and polygons. (WIKIPEDIA) An image is described as a series of geometric shapes. Vector graphics work by describing the grid points at which lines or curves are to be drawn.
Vector graphics "understand" what they are – a square "knows" it is a square and text "knows" that it is text. Because they are objects rather than a series of pixels, vector objects can change their shape and colour, whereas raster graphics cannot. (EISENBERG 2002, p. 2)

Vector Graphics

When zooming vector graphics the quality of the graphic is not getting reduced.

Experience it in the following graphic. Set mouse cursor over graphic, right click and choose "Zoom In" to get a zoomed view of the graphic (This function doesn't exist in Firefox). Do this step several times to zoom in very close and see that the quality of the image is not getting reduced.
To reach the original picture size, right click and choose "Original View".

To visualise vector graphics in the World Wide Web plugins are often required. For example, this SVG vector graphic is visualised in the Internet Explorer with the Adobe SVG Viewer plugin since this browser does not support the vector graphic standard.