There are two basic kinds of graphics. Graphics based on pixels; the dots on the screen and those based on mathematical formulas.
These are always bitmapped or rasterised. Many designers create their original artwork in a vector program such as FreeHand or Illustrator and then open it in PhotoShop or a similar program to rastersie it or turn it into a bitmap.
Bitmapped graphics are created by changing the colour of individual
pixels on the screen - the bits of information are mapped to the pixels
on the screen.
The image of the puzzled screen bean from Word Clipart is a bitmapped image. When the image is viewed closely using a zoom in feature the pixels can be clearly seen. The ragged edge of the image identifies it as a bitmapped graphic.
Vector graphics are generally smooth edged because the shapes are mathematically
defined instead of being mapped to individual pixels.