When you do this the bottom half of the screen is drawn using the new image while the top half still has the old image. This visual effect is called tearing or shearing. In the dark days of DOS you would have had to check for a vertical retrace to determine when the screen was refreshing so that you could avoiding this tearing from happening. With DirectX this check is taken care of for you. Bitmaps and Sprites - Bitmaps are basically images.
Sprites are the same as bitmaps but usually have transparent areas.
The term Sprites, is also used for animated images within a game. Notice how each frame depicts a particular angle of movement. Also note that the transparency colour of this sprite is black, hence the white background above shows through. If you used DirectX without clipping you would be able to draw anywhere on the screen. This is fine if you are in full screen mode, but is definitely unacceptable if your application is windowed.