Mini DisplayPort is a compact version of the DisplayPort connector introduced by Apple in 2008. Mini DisplayPort is free to license, and in 2009 it was included in the official DisplayPort 1.2 spec. In 2011 Apple and Intel announced the Thunderbolt format, which used the same physical connector, but significantly different protocols.
Screen refresh rate is the number of times an image on any type of monitor or television is reconstructed per second. This is measured in hertz.. (Hz).
This tells your GPU to synchronize its actions with the display, which forces it to render and send a new frame when the monitor is ready to redraw the screen. This does limit your framerate exactly to the refresh rate. For example, if your refresh rate is 60Hz, VSync will cap your framerate to 60 FPS.