Refresh rate (measured in Hz, or "Hertz") refers to the capability of a monitor to show multiple frames per second. A monitor with a 60Hz refresh rate updates the displayed image 60 times per second.
Many monitors now offer higher frame rates above the classic 60Hz. Some commonly supported higher refresh rates are 75Hz, 100Hz, 120Hz, 144Hz, 165Hz, 240Hz, and even as high as 360Hz. Even moving from a 60Hz display to a 144Hz display can offer a significant improvement in viewing experience.