parentheses after an alias name

Question

I came across a neat article about using generate_series to create table data. the author does a great job explaining the code, there is however some things I still don't understand. the x after the alias comp3syl(x) and z2(x) is that assigning the derived table's column name to x? Also what is this syntax called? I'm having trouble googling it's documentation without some keywords

SELECT(
SELECT concat_ws(' ',name_first, name_last) as generated
FROM (
    SELECT string_agg(x,'')
    FROM (
        select start_arr[ 1 + ( (random() * 25)::int) % 16 ]
        FROM
        (
            select '{CO,GE,FOR,SO,CO,GIM,SE,CO,GE,CA,FRA,GEC,GE,GA,FRO,GIP}'::text[] as start_arr
        ) syllarr,
        -- need 3 syllabes, and force generator interpretation with the '*0' (else 3 same syllabes)
        generate_series(1, 3 + (generator*0))
    ) AS comp3syl(x)
) AS comp_name_1st(name_first),
(
    SELECT x[ 1 + ( (random() * 25)::int) % 14 ]
    FROM (
        select '{Ltd,& Co,SARL,SA,Gmbh,United,Brothers,& Sons,International,Ext,Worldwide,Global,2000,3000}'::text[]
    ) AS z2(x)
) AS comp_name_last(name_last)
)
FROM generate_series(1,10000) as generator

for anyone interested here is the link to the article: https://regilero.github.io/postgresql/english/2017/06/26/postgresql_advanced_generate_series/

Answer 1

From the documentation:

Another form of table aliasing gives temporary names to the columns of the table, as well as the table itself:

FROM table_reference [AS] alias ( column1 [, column2 [, ...]] )

If fewer column aliases are specified than the actual table has columns, the remaining columns are not renamed. This syntax is especially useful for self-joins or subqueries.

In the code you gave the generate_series() calls aren't aliased in the subqueries themselves so the author names them when he aliases the subquery.