In Joomla, Lock means that the item is currently opened by any user for editing. The lock automatically removes when user clicks on "Save", "Save and Close" and "Cancel" button. If user not click on "Save" or "Close" buttons and instead click on "Back" button to navigate to another page, then the item remains locked. Locka basically appears next to the Joomla modules, Articles, Menu Items, etc.

There are various ways to remove lock:

1. By contacting to the person that has opened the item for editing if they are done with the item. This you can find out by placing the cursor above the lock. It will display a tootilp with the user name who checked out the article.
2. If you have the administrative rights to access the back-end of Joomla site. You can simply clicks on the lock and the lock removes.
3. you can globally remove the lock by clicking on the System -> Global Check-In
4. Maintenance : Global Check-In page appears with the check in information. Select the table name from the list that you wants to check in. Now click the Check In button given at the top left corner of the page. All the items that you have selected are successfully checked in.