An alias is a name someone uses instead of their real one. When a spy goes undercover, she might use an alias so enemies won't discover her true identity. When an author wants privacy, he might publish books under an alias (also called a pen name).

An alias is another name for the same person. Criminals often use aliases to hide from police. Witnesses in dangerous trials sometimes live under aliases to stay safe. Online, people use aliases as usernames to protect their privacy.

You might encounter the word in detective stories or spy novels, where figuring out someone's real identity behind their alias becomes part of solving the mystery. If you heard that someone was “going by the alias of Smith,” it means Smith isn't their real name.

In computer systems, an alias can also mean a shortcut or alternate name for a file, command, or email address, working like a nickname for something technical. Either way, an alias always points to something real while using a different name.