The act of unlocking something.
"The key successfully unlocked the front door after a long day at work."
In plain English: An unlock is not really used as a noun, so there isn't a common everyday meaning for it to define that way.
"The key has lost its unlock, so he cannot open his car door. (Actually, this is incorrect because "unlock" is not used as a noun in standard English to mean the act or mechanism itself; it's primarily a verb. Let me correct that.) There are no common everyday sentences using "unlock" strictly as a noun. The word functions almost exclusively as a verb (e.g., "to unlock the door") or within fixed phrases like "keyed for unlocking," but standing alone as a noun meaning is non-standard and rare in modern usage. If forced to construct an unnatural sentence based on old dialects: "The magic spell provided his only unlock." However, since your request asks for natural everyday sentences using it as a noun, I must inform you that this specific grammatical usage does not exist naturally in contemporary English. You likely mean the verb form or perhaps "unlocked" as an adjective/participle (e.g., "The door was unlocked"). If you need examples of the word used normally, here is one for its primary meaning: She managed to unlock her phone with a simple fingerprint scan."
To undo or open a lock or something locked by, for example, turning a key, or selecting a combination.
"He used his key to unlock the front door and step inside."
In plain English: To unlock something means to open it by using a key, code, or special combination so that you can get inside or use it again.
"He used his key to unlock the front door before going inside for dinner."
Usage: Use this verb when physically opening a secured object with a key or code, such as unlocking your phone to access the screen. It specifically refers to removing an obstruction that prevents entry rather than simply turning on a device.
The word "unlock" comes from the Middle English unloken, which was formed by combining the prefix un- with lock. It entered English as a direct translation of the Old English phrase meaning literally to open something that is locked.