Variable refresh rate

A variable refresh rate (VRR) is the general term for a dynamic display refresh rate that can continuously and seamlessly vary on the fly, on displays that support variable refresh rate technologies.
A display supporting a variable refresh rate usually supports a specific "range" of refresh rates (e.g. 30 Hertz through 144 Hertz). This is called the "variable refresh rate range" (VRR range). The refresh rate can continuously vary seamlessly anywhere within this range.
Purpose.
On displays with a fixed refresh rate, a frame can only be shown on the screen at specific intervals, evenly spaced apart. If a new frame is not ready when that interval arrives, then the old frame is held on screen until the next interval (stutter) or a mixture of the old frame and the completed part of the new frame is shown (tearing). Conversely, if the frame is ready before the interval arrives, then it won't be shown until that interval arrives. A major purpose of variable refresh rates is the elimination of stutters and tearing by keeping refresh rates in sync with a varying frame rate from a video game. This makes display motion more smooth despite a varying frame rate.
Another purpose is power management, by temporarily lowering the refresh rate of a display to save battery power on a laptop or mobile device.
Also, a variable refresh rate allows a display to correctly display any arbitrary film or video frame rate within the refresh rate range supported by a display.
History.
Vector displays had a variable refresh rate on their cathode ray tube (CRT), depending on the number of vectors on the screen, since more vectors took more time to draw on their screen.
More recently, since the 2010s decade, raster displays gained several industry standards for variable refresh rates. Historically, there was only a limited selection of fixed refresh rates for common display modes.
Implementations.
Variable refresh rate display technologies include several industry standards and proprietary standards:
The first phone with VRR was the Samsung Galaxy Note 20 Ultra.