The system catalog table pg_class catalogs tables and most everything else that has columns or is otherwise similar to a table (also known as relations). This includes indexes (see also pg_index), sequences, views, composite types, and TOAST tables. Not all columns are meaningful for all relation types.

column	type	references	description
relname	name		Name of the table, index, view, etc.
relnamespace	oid	pg_namespace.oid	The OID of the namespace (schema) that contains this relation
reltype	oid	pg_type.oid	The OID of the data type that corresponds to this table's row type, if any (zero for indexes, which have no pg_type entry)
reloftype	oid	pg_type.oid	The OID of an entry in pg_type for an underlying composite type.
relowner	oid	pg_authid.oid	Owner of the relation
relam	oid	pg_am.oid	If this is an index, the access method used (B-tree, Bitmap, hash, etc.)
relfilenode	oid		Name of the on-disk file of this relation; 0 if none.
reltablespace	oid	pg_tablespace.oid	The tablespace in which this relation is stored. If zero, the database's default tablespace is implied. (Not meaningful if the relation has no on-disk file.)
relpages	int4		Size of the on-disk representation of this table in pages (of 32K each). This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and a few DDL commands.
reltuples	float4		Number of rows in the table. This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and a few DDL commands.
relallvisible	int32		Number of all-visible blocks (this value may not be up-to-date).
reltoastrelid	oid	pg_class.oid	OID of the TOAST table associated with this table, 0 if none. The TOAST table stores large attributes "out of line" in a secondary table.
relhasindex	boolean		True if this is a table and it has (or recently had) any indexes. This is set by CREATE INDEX, but not cleared immediately by DROP INDEX. VACUUM will clear if it finds the table has no indexes.
relisshared	boolean		True if this table is shared across all databases in the system. Only certain system catalog tables are shared.
relpersistence	char		The type of object persistence: p = heap or append-optimized table, u = unlogged temporary table, t = temporary table.
relkind	char		The type of object r = heap or append-optimized table, i = index, S = sequence, t = TOAST value, v = view, c = composite type, f = foreign table, u = uncatalogued temporary heap table, o = internal append-optimized segment files and EOFs, b = append-only block directory, M = append-only visibility map
relstorage	char		The storage mode of a table a= append-optimized, c= column-oriented, h = heap, v = virtual, x= external table.
relnatts	int2		Number of user columns in the relation (system columns not counted). There must be this many corresponding entries in pg_attribute.
relchecks	int2		Number of check constraints on the table.
relhasoids	boolean		True if an OID is generated for each row of the relation.
relhaspkey	boolean		True if the table has (or once had) a primary key.
relhasrules	boolean		True if table has rules.
relhastriggers	boolean		True if table has (or once had) triggers.
relhassubclass	boolean		True if table has (or once had) any inheritance children.
relispopulated	boolean		True if relation is populated (this is true for all relations other than some materialized views).
relreplident	char		Columns used to form “replica identity” for rows: d = default (primary key, if any), n = nothing, f = all columns i = index with indisreplident set, or default
relfrozenxid	xid		All transaction IDs before this one have been replaced with a permanent (frozen) transaction ID in this table. This is used to track whether the table needs to be vacuumed in order to prevent transaction ID wraparound or to allow pg_clog to be shrunk. The value is 0 (InvalidTransactionId) if the relation is not a table or if the table does not require vacuuming to prevent transaction ID wraparound. The table still might require vacuuming to reclaim disk space.
relminmxid	xid		All multixact IDs before this one have been replaced by a transaction ID in this table. This is used to track whether the table needs to be vacuumed in order to prevent multixact ID wraparound or to allow pg_multixact to be shrunk. Zero (InvalidMultiXactId) if the relation is not a table.
relacl	aclitem[]		Access privileges assigned by GRANT and REVOKE.
reloptions	text[]		Access-method-specific options, as "keyword=value" strings.

Parent topic: System Catalogs Definitions