Monitors have fixed refresh rates meaning that they are locked into displaying a constant frame rate (60HZ=60FPS, 144HZ=144FPS, etc). However GPU’s have a variable frame rate which changes depending on the scene that it’s rendering, so often times what can happen is that as the screen is being refreshed on the monitor, the GPU will send out a new frame that it just rendered resulting in two frames that don’t match up with each other. This is called screen tearing. Free-Sync gets rid of stuttering and tearing by dynamically adjusting the refresh rate of the monitor to match the frame rate of the GPU, so the monitor is always displaying one frame at a time.