What does it mean when says must be at least 4 characters long?

"Must be at least 4 characters long" means that the input you're providing (like a username, password, or answer to a question) needs to have a minimum of 4 characters.

Here's a breakdown:

* Characters: These are individual letters, numbers, or symbols.

* At least: This means the minimum requirement, not the maximum.

* 4 characters long: The input needs to have 4 or more characters in it.

Example:

* "abc" is not valid because it has only 3 characters.

* "abcd" is valid because it has 4 characters.

* "abcdefg" is valid because it has 7 characters, which is more than the minimum of 4.

This rule is often used for security reasons, as longer passwords and usernames are generally harder to guess.