If you have forgotten it, it's really straightforward to reset it.
YOU NEED TO REMEMBER THE APPLE ID USERNAME AND PASSWORD YOU USED!
1) Install iTunes if you haven't already.
2) Put your iPad in restore mode. (I'll provide a link to how to if you don't know.)
3) Plug it into your computer, and iTunes will pop up saying restore and update your device.
4) Wait till your device resets.
DON'T PLUG IT OUT, EVEN IF IT MAY SEEM TO BE STUCK, IT'S NOT! YOU'LL GET AN ERROR IF IT IS!
5) By now your device has reset, passcode has been removed and now you can setup your device like you first got it.
6) You will have entered your Apple ID, at the start, if you don't remember it, reset it, otherwise your still locked out.
If this is all confusing, contact Apple (1-800-MY-APPLE)
Note: There is no way to retrieve the data on your iPad if it has been locked out unless you had backed it up previously.
If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support- Restore mode steps.