Access control list (ACL) is a set of rules that define the permissions granted to users or system processes for accessing specific resources, such as files, directories, or network devices. Each entry in an ACL specifies a subject (user or process) and the level of access allowed (e.g., view, edit, print). ACLs are used to enforce security policies by ensuring that only authorized users can perform certain actions on sensitive data and systems. By clearly delineating access rights, ACLs help protect against unauthorized access, data breaches, and ensure compliance with security regulations.