Here Min no.of days related to password change
i'll explain you in brief if you set MIN_DAYS value to zero then that user could change his/her password at any point of time.
If you set any value to MIN_DAYS then the user has to wait min_days for password change.
If user tries to reset password before minimum_days set, he/she will get error as listed below.
Changing password for test.
(current) UNIX password:
You must wait longer to change your password
passwd: Authentication token manipulation error
passwd: password unchanged