Text sometimes exhibits case sensitivity, that is, words can differ in meaning based on the differing use of uppercase and lowercase letters. Words with capital letters don't always have the same meaning as words with lowercase letters.

When a computer compares two words to decide whether they are equal, it may or may not consider words equal which only differ in case.

Often, computer passwords are case sensitive and computer user names are not, which can be confusing for the inexperienced user. Passwords are often made case sensitive to make them harder to guess, whereas making usernames harder to guess or remember is not an advantage.