login/min_password_diff is a SAP Parameter attribute which is used to control min. number of chars which differ between old and new password 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 .
The administrator can use this parameter to specify by how many
characters a new password must differ from the old password when the
user changes it. This parameter is ignored when new users are created or
when passwordsd are reset to the initial password.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.