Actually it's in hz, and quite simply it's how many times your monitor updates the screen image per second. Generally, the higher you go the better and the easier it is on the eyes. Most people find 60 bad (lots of flicker, can cause headaches) but from what I've read, 85hz+ is ideal for CRT, maybe 60-75 for LCD (different technology)?
Either way, the higher the better though it does depend a lot on the person aswell.
im on 1024x768 at 60Hz..not-so-new toshiba satellite notebook. anyway from a certain point onwards the human eye cannot detect the refresh rates so any monitor advertising hilarious rates just means that its good enough to serve ur purpose