Screen Tearing is a visual artifact.

What Causes Screen Tearing?

When the frame rate output of a GPU does not match the refresh rate of a monitor causing multiple frames to be displayed at once, this effect is commonly observed in video games and is characterized by one or more horizontal fragmentations of an image during high-motion gameplay. 

How to Fix Screen Tearing?

An easy fix for screen tearing in video games is to enable VSync using in-game settings which will limit your frame rate to the refresh rate of your monitor automatically. Some monitors come equipped with G-Sync or FreeSync technology which will sync the display's refresh rate with your graphics card system-wide.