What is the difference between CHARACTER VARYING and VARCHAR in PostgreSQL?

VARCHAR is an alias for CHARACTER VARYING, so no difference, see documentation 🙂

The notations varchar(n) and char(n) are aliases for character varying(n) and character(n), respectively. character without length specifier is equivalent to character(1). If character varying is used without length specifier, the type accepts strings of any size. The latter is a PostgreSQL extension.

Note on capitalization: The PostgreSQL documentation uses the all lower case stylization: character varying. In contrast the official SQL standard uses the stylization with all caps throughout its 1000 pages: CHARACTER VARYING.