The view pg_shadow exists for backwards compatibility: it emulates a catalog that existed in PostgreSQL before version 8.1. It shows properties of all roles that are marked as rolcanlogin.
The name stems from the fact that this table should not be readable by the public since it contains passwords. pg_user is a publicly readable view on pg_shadow that blanks out the password field.
Table 43-45. pg_shadow Columns
|ID of this user
|User may create databases
|User is a superuser
|User may update system catalogs. (Even a superuser may not do this unless this column is true.)
|Password (possibly encrypted)
|Password expiry time (only used for password authentication)
|Session defaults for run-time configuration variables