Vendors Making the DB Sound 10 Larger Than They Are
Irrelevant disk - which has nothing to do with the database.
Redundant disk - only there for data protection
Freespace - for workspace or future database growth
Summary data - precomputed aggregates that are stores so queries can be serviced quickly
Indexes - which are structures to maintain the database engine to speed access to the data
User data - actual information content of the database