Display Refresh Rate refers to number of times the screen refreshed to draw. Usually it will be measured in Hz eg. 60Hz, 90Hz, 120Hz. Most of the smartphones uses 60Hz refresh rate, but some high-end and gaming focused phones comes with 90 Hz or 120 Hz refresh rate.
Higher screen refresh rates will improve the scrolling smoothness and quick rendering animations. At the same time it will also consume more battery power than regular 60Hz refresh rate.