Flash Templates Tutorials - Vector and Bitmap Graphics in Flash - Bitmap graphics
Bitmap graphics describe images using colored points, called pixels, located on the grid. For example, the image of a tree leave is described by the specific location and the color of each grid point, which creates an image almost the same as in mosaic.
When editing bitmap graphics, you edit pixels and not the lines. Bitmap graphics depends on the resolution, since data describing the image is attached to the grid of a certain size. When editing bitmap graphics, its quality may be changed. In particular, changing the size of bitmap graphics could lead to "shaggy" image edges, as pixels will be redistributed on the grid. Displaying bitmap graphics on devices with low resolution rather than resolution of the image itself, will lower its quality