A username is the unique name you choose to identify yourself on a computer system, website, or app. When you create an account for an online game, your school's computer network, or a website, you pick a username so the system knows who you are when you log in. It's like having a special nickname that belongs only to you on that particular service.

Most usernames combine letters and numbers, like “ChessPlayer2015” or “MiaSoccer23.” Some systems have rules about what you can use: they might not allow spaces, require a certain length, or prevent you from choosing a username someone else already has. That's why you often see numbers added to the end of usernames, because “Sarah” might already be taken, so you might need to use “Sarah127” instead.

Your username is paired with a password, which you keep secret. Think of it like this: your username is like writing your name on the outside of your locker so everyone knows it's yours, while your password is like the secret combination that only you should know. Together, they protect your account and help you access your information safely. Many people use different usernames on different websites, which helps keep their online activities separate and organized.