The second pane in the system settings window lets you specify any mandatory rules or requirements that user passwords must meet. Among the possible parameters you can specify are:
Minimum password length - 0 means no minimum and a positive number (x) means the password must contain a minimum of x characters
Previous passwords remembered - 0 remembers none and a positive number (x) remembers that many previous passwords, which must be different than a new password the user enters
Require special characters - requires a password to contain at least one special non-alphanumeric character (!, , @, #, $, %, ^, &, *, (, ), _, and +)
Max login attempts - 0 means no checking, a positive number (x) means that no more login attempts can be made or the account will be locked.
Prevent multiple simultaneous logins - yes or no
Max days between logins - 0 means no checking and a positive number (x) indicates the maximum number of days that can elapse between logins without the account's being disabled.
Password expiration time (in days) - 0 means no expiration and a positive number (x) indicates the number of days before a new password is required
Password expiration warning time - number of days before password expiration that the user is warned and prompted to change the password.