Glossary
PAM (Pluggable Authentication Modules)
A modular framework that lets Linux services delegate authentication, account, and session policy to stackable, configurable modules.
PAM (Pluggable Authentication Modules) is a framework that separates how programs authenticate users from the applications themselves. Services like login, sshd, and sudo call PAM, which consults a stack of modules handling authentication, account validation, password rules, and session setup. Administrators change policy by editing configuration rather than recompiling software.
For hardening it is the central place to enforce password complexity, account lockout after failed attempts, and two-factor checks. Configuration lives under /etc/pam.d/, with one file per service.