An object is locked when it is opened by a user, which prevents other users from modifying the object at the same time.
For example, if more than one user wants to open a topic, the first user to open the topic can edit it. For other users, the topic will open as read only. In the Editor, a message opens next to the topic name to explain that the topic has been locked. In the object list, the object appears with a lock icon.
When the first user closes the topic, the lock icon goes away and another user can open the topic for editing.