X-SecondarySection
The pkg_explorer tool makes use of two categorizations, X-PrimarySection and X-SecondarySection, in order to build a directed acyclic graph of all the packages available in a way that makes it easy to find packages.
The Secondary Section represents what is also called the Sub-Section. It is a quite specific category creating small group of software such as "shut them up" and "role playing games" for software under the Games section.
We do not impose any naming convention so if you are creating your own environment, you can use anything that makes sense to you.
For additional information, you may want to read more about the Component field.