Locks are used to prevent multiple people from working on the same file and writing over each other's work. A lock is set automatically when a user "Edits" a file or when a file is modified via import or upload.

When you own the lock, a key  is shown beside the file. When someone else owns the lock, a padlock  icon is shown.

Locks can be unlocked by the person who owns the lock or the administrator for your ministry.

To find out who owns the lock, use the File > File Properties drop-down selection and find out the user who has the file locked. In the below image, aengler has the file locked in the truthmedia workarea.