Raster (or bitmap) images are described by an array or map of bits within a rectangular grid of pixels or dots. Vector images are described by lines, shapes, and other graphic image components stored in a format that incorporates geometric formulas for rendering the image elements.
Raster (bitmap) image: At 100% the image looks almost the same as the vector version (below). Notice that as soon as the image is scaled, the pixels on the edge begin to show and the edges no longer look smooth.
Vector image: The vector image is created by defining points and curves. (This vector image was created using Adobe Illustrator.) When vector graphics are scaled, the edges remain crisp and sharp no matter the size.