In UBIK, a MetaClass is used to define the appearance and behavior of a certain set of future content objects.
A MetaClass can, and actually has to, inherit from another MetaClass. This can be a built in UBIK System-MetaClass, which is typically the case when customizing starts in an "empty" data model. Of course, and more likely, it will be another MetaClass that was already created during customizing.