Unauthorized means done without official permission or approval. When you take your friend's bike without asking, that's unauthorized use. When someone accesses a computer system they're not supposed to enter, that's unauthorized access.

Think of authorization as official permission: your teacher authorizes you to go to the library, your parents authorize you to stay at a friend's house, or a security guard authorizes visitors to enter a building.

Something unauthorized happens when someone acts without getting that permission first. A student making unauthorized copies of a test answer key is doing something they know they shouldn't. An unauthorized biography means the book's subject never approved it or cooperated with it.

You'll often see “authorized personnel only” signs in places like construction sites, backstage areas, or restricted parts of buildings. These signs mean only people with official permission can enter. Anyone else entering would be there in an unauthorized capacity.

The word carries a sense of rule-breaking or boundary-crossing. While not every unauthorized action is equally serious (borrowing a pencil without asking versus breaking into someone's locker), the term indicates that proper permission wasn't obtained. In many contexts, especially legal or security-related ones, unauthorized actions can lead to serious consequences.