Bitmap means a map of bits (or pixels) that form a picture. Thus, a bitmapped image is an image comprised of pixels. Though bitmaps store images in high resolution, they do not rescale very well, and tend to appear jagged when zoomed in, and blurry when reduced in size. Bitmaps are ideal for storing digital images. Whereas a bitmapped image will lose clarity when rescaled, a vector graphic can be scaled indefinitely without losing clarity.
The example below shows the effect of a bitmap graphic versus a vector graphic. When zoomed in, the bitmapped image appears jagged, whereas the vector graphic appears clear and crisp.