Refresh Rate and VSYNC

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=239

The refresh rate setting determines how many times your display is illuminated every second. This is distinct from the measure of frame rate per second (FPS) in that the refresh rate includes the repeated illumination of identical frames, while the FPS is a measure of how often a display can change from one image to another.

Please follow these steps if you would like to change the refresh rate for your display:

1. Right-click on the Windows desktop and select Properties
2. Select the Settings tab
3. Click the Advanced button near the bottom of the window
4. Select the Monitor tab and then pick a Screen refresh rate from the drop-down menu
5. Click OK to test your settings

The VSYNC setting determines whether or not Windows will allow your games and other applications to display different images at frame rate (FPS) which exceeds your refresh rate. (If you have disabled VSYNC you may experience visual "tearing" and video artifacts while playing, as you will not see all of the frames which are being rendered)

Please see the Troubleshooting Gameplay and Performance topic if you would like to optimize game performance on your machine.