Q: what is passcode?

A 4-digit PIN number used to lock your devices Lock Screen. If your forgot yours:

Locked Out, Forgot Lock or Restrictions Passcode, or Need to Restore Your Device: Several Alternative Solutions

A

1. iOS- Forgotten passcode or device disabled after entering wrong passcode

2. iPhone, iPad, iPod touch: Wrong passcode results in red disabled screen

3. Restoring iPod touch after forgotten passcode

4. What to Do If You've Forgotten Your iPhone's Passcode

5. iOS- Understanding passcodes

6. iTunes 10 for Mac- Update and restore software on iPod, iPhone, or iPad

7. iOS - Unable to update or restore

Forgotten Restrictions Passcode Help

            iPad,iPod,iPod Touch Recovery Mode

You will need to restore your device as New to remove a Restrictions passcode. Go through the normal process to restore your device, but when you see the options to restore as New or from a backup, be sure to choose New.

You can restore from a backup if you have one from BEFORE you set the restrictions passcode.

Also, see iTunes- Restoring iOS software.

a passcode is a lock that you can put on your device, usually right when you turn it on, that prevents someone that doesn't know the code from using your device.

You can use a simple 4 number passcode or you can use a longer letter/number combination

A passcode is something you can set, a four-digit number, to keep others from using your iPad. 

If you have forgotten your passcode you have to restore using the recovery mode instructions in http://support.apple.com/kb/HT1212