Oracle SQL Plan operation BITMAP CONVERSION FROM ROWIDS

create table tq84_tab (
   val_1    number,
   val_2    number,
   pad      varchar2(100)
);


insert into tq84_tab
select
   mod(rownum, 1001),
   mod(rownum,   10),
   rpad('*', 100, '*')
from
   dual connect by level <= 10010;

--
-- Create an «ordinary» and a bitmap index:
--
create        index tq84_tab_ix_ord on tq84_tab(val_1);
create bitmap index tq84_tab_ix_bmp on tq84_tab(val_2);

begin
   dbms_stats.gather_table_stats(user, 'tq84_tab');
end;
/

explain plan for
select * from tq84_tab where val_1 = 500 and val_2 = 1;

select * from table(dbms_xplan.display(format=>'basic'));
--
-- ---------------------------------------------------------------
-- | Id  | Operation                           | Name            |
-- ---------------------------------------------------------------
-- |   0 | SELECT STATEMENT                    |                 |
-- |   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| TQ84_TAB        |
-- |   2 |   BITMAP CONVERSION TO ROWIDS       |                 |
-- |   3 |    BITMAP AND                       |                 |
-- |   4 |     BITMAP CONVERSION FROM ROWIDS   |                 |
-- |   5 |      INDEX RANGE SCAN               | TQ84_TAB_IX_ORD |
-- |   6 |     BITMAP INDEX SINGLE VALUE       | TQ84_TAB_IX_BMP |
-- ---------------------------------------------------------------

drop table tq84_tab;