The range of pictures, drawings and images which can be produced by a computer are called graphics. The main types of graphics packages are painting, drawing, photo editing and CAD.
Bitmap graphics made with painting packages consist of many tiny dots called pixels. It is possible to edit each individual pixel.
Since the computer has to store information about every single pixel (the colour for example) in the image, the file size of a bitmap graphic is often quite large. Bitmap graphics lose quality when they're resized.