Domains
Domains behave as data types with optional built-in constraints.
User-defined types
User-defined types are objects that create new data types that can be used by other objects in the database.
Casts
Casts are objects used to convert values between two different data types.
Collations
Collations are objects that allow for the sorting mode and character classification behavior to be specified either per column or per operation.
Conversions
Conversions are objects used to perform transformations between two different encodings.
Operators
Operators are one of the most powerful objects implemented by PostgreSQL as an extension of the SQL standards.
Operator classes
Operator classes define how indexes can handle a specific data type.
Operator families
Operator families define a collection of related operator classes, operators, and support functions.