That's screen tearing.
You need to cap your FPS according to the refresh rate of your monitor to stop it.
Or, if there is no option to cap your FPS, turn on VSync.
1 Hz is roughly the equivalent of 1 FPS.
So if you have a 60 Hz monitor, cap FPS at 60.
If you have a 144 Hz monitor, cap FPS at 144 FPS.
Etc, etc.