You've already seen mention of some useful kinds of Mts (microtheories, contexts). Lets look at the main kinds in more detail. The main kinds of Mt are:
#$GeneralMicrotheory
These are contexts which are likely to have repeated uses, by many
different users; they often relate to a particular cultures, societies, or
application areas.
#$BaseKB
This Mt is the ``base'' upon which all others are built. All Mts have
access to the #$BaseKB via the #$genlMt relation. The #$BaseKB contains
fundamental information that is expected to be potentially useful in all
situations, cultures and applications.
#$EverythingPSC This is the opposite extreme; #$EverythingPSC has no information of its own, but it has access to all the information in all of the other Mts. It is an artificial context created to enable a person (using the browser) to explore the whole Cyc Knowledge Base. Cyc itself never operates in #$EverythingPSC as its current context.