Vsync
Holding off the frame buffer swap until the display has finished its refresh — cures tearing, but at a cost.
The graphics card holds the finished frame back until the next vertical blanking interval, the moment between two display refreshes. No seam appears, because the display never reads a buffer that is swapped mid-scan.
Two drawbacks follow. If the card cannot finish before the next interval it must wait a whole cycle more, which can halve the frame rate from 60 to 30 in one step. And the forced wait adds input latency, which is why competitive players turn it off. Triple buffering eases the first problem, and adaptive synchronisation solves both by making the display wait instead.