SQL & PL/SQL

create type a_b_type as object (
a number,
b varchar2(10)
);

create type a_b_table as table of a_b_type

create table a_b_t (
a number,
b varchar2(10)
)


insert into a_b_t values (1, 'one');
insert into a_b_t values (2, 'two');
insert into a_b_t values (3, 'three');
insert into a_b_t values (4, 'four');
insert into a_b_t values (5, 'five');
insert into a_b_t values (6, 'six');
insert into a_b_t values (7, 'seven');
insert into a_b_t values (8, 'eight');


declare
v_a_b_table a_b_table;
begin
select
cast(
multiset(select * from a_b_t) as a_b_table
)
into v_a_b_table
from
dual;

for r in (
select
a,b
from
table(v_a_b_table)
where a = length(b)-2) loop
dbms_output.put_line(r.a || ' ' || r.b);
end loop;
end;


Someone please tell me,
what this mean:

cast(
multiset(select * from a_b_t) as a_b_table

Thanks.