VRR, or simply Variable Refresh Rate, is a feature on monitors, TVs, and other types of displays that significantly improves the viewing experience from games to movies to web browsing.
What is variable refresh rate?
Variable refresh rate is a technology that allows your monitor or TV to dynamically adjust its refresh rate based on the frame rate of the content you are viewing. Every monitor needs to refresh its image once per second, this is the refresh rate (measured in Hertz). Similarly, movies, TV shows, and games all display frames per second (fps).
In an ideal world, your refresh rate and frame rate would always match, but in most cases this won't be the case. Your refresh rate and frame rate often become out of sync, especially in video games, which can cause some nasty visual issues (more on this in the next section).
When viewing a piece of media, the number of images you see depends on the frame rate of the media itself and the refresh rate of your monitor. The slowest is the speed at which you see the media. So if you watch a movie at 24 fps on a 144Hz monitor, you'll watch the movie at 24 fps. However, if you play a game like Counter-Strike: Global Offensive on a 60Hz monitor, you'll only see 60 fps even if the game runs at 100 fps or even 1,000 fps. A high refresh rate monitor will display more unique frames.
Screen tearing problem
When media is run at a frame rate that is not equal to the monitor's refresh rate, it can cause screen tearing, a very ugly visual error that occurs when the monitor is forced to display two different frames at the same time. For example, 30 or 60 fps video viewed on a 60Hz monitor will not exhibit screen tearing, but 35 fps video will.
Screen tearing wasn't really an issue for a while because everything we watched had frame rates appropriate to the monitor: 30 and 60 fps for home TV, 24 fps for theater movies. But as gaming (especially on PC) becomes more and more popular, screen tearing becomes more and more of an issue for people.
The unique thing about PC games is that there are almost unlimited combinations of PC parts to play the game. But the thing is, you can never expect to hit perfect 30 or 60 fps every moment of every game. Even if you run at a constant frame rate, you'll still get screen tearing unless you get exactly 30 or 60 fps. For years, VSync was the only way to fix tearing in games, but what VSync did was basically limit the frame rate, and no one liked that. Choosing between a higher frame rate and screen tearing or a lower frame rate is never fun.