An unlocked door or lock means that it's not secured with a key or code. It can also mean that something was previously locked but now has access to information or abilities.
When people talk about an unlocked phone, they're usually referring to a device that wasn't tied to a specific carrier or had its restrictions removed so you could use any SIM card. This is often done when buying a used phone, and it's a good thing because you won't be locked into a contract with the original owner's network. Unlocked phones are also popular among travelers who need to switch between different countries' networks. On the other hand, an unlocked puzzle means one that has been solved or made easier to understand.
To undo or open a lock or something locked by, for example, turning a key, or selecting a combination.
Example: I unlocked the door and walked in.
Not secured or protected by a lock.
Example: an unlocked computer file
