I found this link and book on G+ today. It looks like a great primer for learning SELinux. What is SELinux? SELinux is a security layer used by several different Linux Distributions to isolate applications from the lower level parts of Linux. It does this by blocking access to certain functions until you grant it access. As long as the applications you grant access to aren't infected with a virus or have a security hole it helps alot. If an approved application does have a problem it prevents it from going beyond the boundaries it is set for.
Yeah the book does a better job of explaining it. So go check it out.