Other forms: unlocked; unlocking; unlocks
When you unlock something, you turn a key or use a code in order to open it. You have to unlock your locker before you can get the books you need for English class.
You might unlock your front door by turning a bolt or unlock a hotel room door by sliding a card into a reader. Either way, something was secured with a lock and now you've opened it. This verb is also used for smart phones: "Once you unlock the screen, you can see that photo I sent." Unlock is formed by adding the prefix un-, "reverse," to lock, "fasten or secure."