It's a proprietary nVidia technology that essentially does reverse V-Sync. Instead of having the video card render a frame and wait for the monitor to be ready to draw it like normal V-Sync, the monitor waits for the video card to hand it a finished frame before drawing, keeping the old frame on-screen as long as needed. The article goes into a little more detail; they take advantage of the VBLANK interval (legacy from the CRT days) to get the display to act like this.
It's a proprietary nVidia technology that essentially does reverse V-Sync. Instead of having the video card render a frame and wait for the monitor to be ready to draw it like normal V-Sync, the monitor waits for the video card to hand it a finished frame before drawing, keeping the old frame on-screen as long as needed. The article goes into a little more detail; they take advantage of the VBLANK interval (legacy from the CRT days) to get the display to act like this.