I'm seeing this available on higher end disc players and as I'm a noob, I need some explanation of what it is, what it does, and how important it is to have.
Thanks

Well, I guess Semi_On will fill in here as soon as his "clock" allows. But it suffices to say that ALL digital players have an internal clock generator, to which the timing of all the 1s and 0s they send out are synchronized. A special "clock module" is most likely a meaningless marketing hype for that brand(s) of "high-end" players.

Can you provide a link? Going on nothing other than what you've typed, I'd assume it's some sort of reference clock for the other hardware. If that's the case, don't bother because all your hardware reclocks its activity internally anyway.

Craig, as Masa and Josh pointed out, all CD players have clocks which synchronize their output just fine and have mistiming "jitter" at an inaudibly low level. This is true regardless of whether the player cost $5,000 or $50. I've read some nonsense relating to add-on clock modules which purport to reduce jitter so that the "tempo" of the music is much improved. More snake-oil; save your money.

Thanks. I've seen it advertised specifically on the cambridge audio D300 se disc player. here's the link:
http://www.cambridgeaudio.com/index2_f.htm