A 120hz monitor means a monitor which has a 120Hz refresh rate. Monitors are divided with various refresh rates such as 60hz, 75Hz, 120Hz, 140Hz, etc. The best 120 Hz monitor is for the people who enjoy and experiences the best gaming. People who are avid gamers must go with a 4k or 1080p 120Hz monitor.The refresh rate measures how quickly or fastly the monitor display the content on the screen refreshes. Although it is measured in Hertz (Hz), the refresh rate counts the number of times the display refreshes every second it is on. For example, a 60Hz display refreshes 60 times per second, 90Hz is 90 times per second, and 120Hz is 120 times per second. So a 120Hz display refreshes twice as fast as a 60Hz panel and 4x faster than an old 30Hz display.