An unlocked padlock used to secure a latch or chain, or as an icon for a non-secure connection or open access online.
Often depicted with a gold base and silver restraints, it can be used to represent a lack of or concern for privacy and security.
It can also be used for a figurative feeling of unlocking, such as unlocking an achievement.
This emoji does not appear in page titles on Apple's Safari web browser, presumably to prevent lesser-known sites from pretending to have HTTPS installed for encryption.