Security-Enhanced Linux (SELinux) is a Linux kernel security module that provides a mechanism for supporting access control security policies.
SELinux is a set of kernel modifications and user-space tools, which have been added to various Linux distributions.
A Linux kernel integrating SELinux enforces mandatory access control (MAC) policies that confine user programs' and system servers' access to files and network resources.
To read more in-depth on mandatory access control (MAC), see this Wiki.
