Pluggable Authentication Module
PAM (Pluggable Authentication Module) was originally developed in 1995 and provides a library, which is a generalized API for authentication-related services. PAM allows a system administrator to add new authentication methods simply by installing new PAM modules, and to modify authentication policies by editing configuration files.
Simply stated, PAM it provides and interface for the interfacing of LDAP
a common authentication scheme that can be used with a wide variety of applications.
significant flexibility and control over authentication for both system administrators and application developers.
a single, fully-documented library which allows developers to write programs without having to create their own authentication schemes.