An access control system is a security solution that regulates and manages entry to a physical or digital space. It typically involves authentication, authorization, and monitoring of individuals' or devices' access. This can include key cards, biometric scans, PINs, or digital certificates for physical access, and username/password combinations or other authentication methods for digital access. Access control systems are commonly used in buildings, data centers, and computer networks to enhance security and control who can enter specific areas or access certain resources.