pg_opclass defines index access method operator classes. Each operator class defines semantics for index columns of a particular data type and a particular index access method. An operator class essentially specifies that a particular operator family is applicable to a particular indexable column data type. The set of operators from the family that are actually usable with the indexed column are whichever ones accept the column's data type as their left-hand input.
Operator classes are described at length in Section 37.16.
Index access method operator class is for
Name of this operator class
Namespace of this operator class
Owner of the operator class
Operator family containing the operator class
Data type that the operator class indexes
True if this operator class is the default for
Type of data stored in index, or zero if same as
An operator class's
opcmethod must match the
opfmethod of its containing operator family. Also, there must be no more than one
pg_opclass row having
opcdefault true for any given combination of