A password strength meter is an indicator, either in graphical or text form, of the strength of a password as entered by a user.
A password strength meter shows how resistant a given password might be to password cracking attempts like brute force and dictionary attacks. Meters have rules they use to assign points for password hardening measures such as including a full combination of symbols, numbers, uppercase and lowercase letters. Simple names and words might receive a deduction in points, as might repeated letters.
Password strength meters are intended to motivate users to create stronger passwords in the interest of tightening security. A study by Blase Ur from Carnegie Mellon University found that the meters do improve user passwords. Their motivating effect was especially high when showing a score numerically and relative to other users.