SELinux (Security-Enhanced Linux) is a type of security software that provides an extra layer of protection for Linux-based operating systems. It enforces mandatory access control policies to restrict access to system resources and prevent unauthorized actions. SELinux uses labels to identify and categorize system objects such as files, processes, and network ports. These labels are used to determine which actions are allowed or denied based on policies set by the system administrator. SELinux can help defend against attacks, reduce system vulnerabilities, and improve overall system security. It is a specialized skill because it involves expertise in understanding and configuring complex security policies for specific applications and systems.