Press the Q key to exit the object descriptions. \dd means "show descriptions of all objects that have descriptions." By default system objects are not shown, so to see these add S.

Postgres is more than a RDBMS; it calls itself an object-relational database management system, or ORDBMS. This is not the same as a object-oriented database management system (OODBMS), but something of a hybrid, a traditional relational database with an object-oriented database model; it supports objects, classes and inheritance.

Let's look at some tables while we're in the postgres DB. First, list its system tables:

postgres=# \dtS