This is something that confuses a lot of people, so I will try my best to explain it.
Vertical sync, frame rate, and refresh rate all have an impact on the quality of your gameplay and they are all connected. First, here are some general definitions:
The refresh rate is the number of times per second that the image on the monitor is refreshed. For RL series monitors, this is will be 60Hz, or 60 times per second. For the XL series, this is typically 144Hz, or 144 times per second.
Frame Rate (or FPS)
The frame rate, also known as FPS (Frames per second) is a measure of how fast the video card is producing frames to send to the monitor. This can vary from 1 to several hundred.