The ability to compare multiple columns (tuples) the same way a single column can be compared
SELECT *
FROM person
WHERE (firstname, lastname) = ( ('Arthur', 'Dent') );
SELECT *
FROM person
WHERE (firstname, lastname) > ('Arthur', 'Dent');
SELECT *
FROM person
WHERE (firstname, lastname) IN ( ('Arthur', 'Dent'), ('Ford','Prefect') )
SELECT *
FROM some_table
WHERE (col_one, col_two) IN (SELECT x,y FROM other_table);