login/min_password_letters is a SAP Parameter attribute which is used to control min. number of letters in passwords information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
This parameter determines the minimum number of letters that a password
must contain. It applies both when assigning new passwords and when
changing the password or resetting passwords.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.