Your iPad may lock (and display a message that it is locked) if you enter the wrong passcode or PIN a few times. Usually the lock will clear in a little while by itself.

However, if you enter the wrong passcode 6 or more times, your iPad will display iPad Disabled and permanently lock. In that case:

1. Follow the instructions in this link to restore your iPad.
2. Then, run the iPad setup process and be sure to choose Restore from iCloud Backup on the Setup Up iPad screen.

Note that the process above will result in you loosing all data created or changed after the last time the iCloud Backup ran on your computer.