PostgreSQL is an advanced Object-Relational database management system (DBMS). The base postgresql package contains the client programs that you'll need to access a PostgreSQL DBMS server, as well as HTML documentation for the whole system. These client programs can be located on the same machine as the PostgreSQL server, or on a remote machine that accesses a PostgreSQL server over a network connection. The PostgreSQL server can be found in the postgresql-server sub-package.
acquired package info from repodata DB: repodata/9fa7a97b004e6cd27df42fe8fada322769689e7d75b9392144123908e6bfdc23-primary.sqlite.bz2
The postgresql-docs package contains some additional documentation for PostgreSQL. Currently, this includes the main documentation in PDF format and source files for the PostgreSQL tutorial.