Self-explanatory if you ask me, but, who knows...
Used via the unlock <target> command.
Unlocking is used to reveal what treasures chests/strongboxes hold inside them. It can also be used to pick the locks of any of the many locked doors around the lands.
In the past, some of the younger generations of Rogues', have been known to use this ability to garner the experience needed to advance themselves within the Guilds ranks.