Access control is a security method that manages who can view, use, or modify particular resources in a computer system. It ensures only authorized users can access specific data only for authorized actions. This involves verifying user identities (authentication), giving the right permissions (authorization), and keeping track of user activities (accountability). Examples include role-based access control (RBAC), where access is based on user roles, and discretionary access control (DAC), where data owners set access rules. Access control is crucial for keeping information safe and secure from unauthorized access and preventing potential breaches.