Tearing is the appearance of the image on your screen to tear during a number of frames. It happens a lot when there is fast action on the screen like turning rapidly. Using Vsync eliminates tearing.
Also, if you overclock your card too high, you may notice artifacts, which look like tearing, in-game. In that case, you must underclock your card until they disappear.
It happens when your video card changes the raster image when the monitor is mid-scan. One scene may be drawn to the top of the screen and another to the bottom, and sometimes more. If you think of each refresh of your monitor as a frame, and the different raster images as frames, then what V-Sync does is synchronize the refreshing of these frames; it ensures that your video card doesn't change the raster image mid-refresh.
OT: Ya just turn on vsync and youll be fine, that vsync does if synchronize your monitorsa refresh rate proly around 70 hz with your FPS so you dont go over it and see the "tearing" effect.