Anything that is case-sensitive distinguishes between uppercase and lowercase letters. In other words, it means that two words that look or sound identical but use different font sizes are not considered the same.

For example, if a password field is case-sensitive, you must enter each font as you did when the password was created. Any tool that supports text input can support case-sensitive input.

Examples of computer-related data that are often, but not always, case-sensitive include commands, user names, file names, programming language tags, variables, and passwords.

For example, because Windows passwords are case-sensitive, the password HappyApple$ is only valid if entered that way. You cannot use HAPPYAPPLE$ or even happyApple$, where even one letter is in the wrong uppercase form. Because each letter can be uppercase or lowercase, any version of the password that uses both uppercase letters is effectively a completely different password.