G-Sync is a technology developed by NVIDIA that synchronizes the monitor's refresh directly to the GPU render rate, allowing images to be displayed the moment they are rendered. This allows for smoother gameplay, eliminates tearing and stuttering, and reduces input lag.
G-Sync technology will be incorporated within some cutting edge gaming monitors in the near future. In the meantime, NVIDIA G-SYNC Do-it-yourself kits for the ASUS VG248QE monitor will be available for purchase later this year.
For more information about G-Sync, please see the G-Sync FAQ