http://www.microsoft.com/windows/products/windowsvista/features/experiences/aero.mspx
When using Windows Aero, open windows glide smoothly on your screen when
you move or resize them. There are no redraw artifacts, latency, or
"tearing" effects that you sometimes see, particularly in windows that
display dynamic content such as video. Using Aero will even reduce legacy
graphics driver-related problems on your system, giving you an even more
confident and stable Windows desktop experience.
http://msdn2.microsoft.com/en-us/library/aa480220.aspx
In Windows XP, applications update their windows directly when the OS
requests them to. These requests could be executed asynchronously with
respect to the refresh rate of the monitor or to any updates that may be
currently running. The effect of these requests is that the user sees
windows tearing and re-drawing incorrectly or slowly. The DWM style of
window presentation eliminates the tearing artifacts, providing a high
quality desktop experience. The benefit to the end user is that the system
appears to be more responsive and the experience is cleaner.
http://en.wikipedia.org/wiki/Page_tearing
Page tearing is a phenomenon in computer and video games where a
previously rendered frame overlaps a newly rendered frame, creating a torn
look as two parts of an object - a wall, for example - don't line up.
In vertical synchronization (V-sync), the previous frame is held before
rendering the next frame, creating a smoother look.
The faster the monitor's response time, the less page tearing, the higher
the monitor's refresh rate, and the higher the frame rate.
http://www.virtualdub.org/blog/pivot/entry.php?id=74
Tearing is a display artifact that occurs when images are presented to the
screen without regard for the current status of the output circuitry. It
occurs because pixels are sent to the screen gradually in book order
rather than instantaneously. What happens is that the output DAC reads
across the same area of the screen that is bring written to, so the
monitor ends up showing a half-updated image. The result is a momentary
frame that has half of an old frame and half of a new one, with a clean
horizontal split across (the tear). Because the location of the tear
varies according to timing, it usually jumps all over the place, which can
be distracting.
http://www.2seetv.co.uk/acatalog/Glossary_of_Terms.html
Tearing - A lateral displacement of the video lines due to sync
instability. It appears as though parts of the images have been torn away.