Oracle SQL Plan operation INDEX UNIQUE SCAN

create table tq84_A (
   nm   number,
   tx   varchar2(200)
);

insert into tq84_A
select
   mod(level * 773, 1009),
   lpad('x', 200, 'x')
from 
   dual connect by level <= 1009;

create unique index tq84_A_uq on tq84_A(nm);

begin
   dbms_stats.gather_table_stats(user, 'tq84_A');
end;
/

explain plan for
select
   tx
from
   tq84_A
where
   nm = 500;

select * from table(dbms_xplan.display(format=>'basic'));
--
-- -------------------------------------------------
-- | Id  | Operation                   | Name      |
-- -------------------------------------------------
-- |   0 | SELECT STATEMENT            |           |
-- |   1 |  TABLE ACCESS BY INDEX ROWID| TQ84_A    |
-- |   2 |   INDEX UNIQUE SCAN         | TQ84_A_UQ |
-- -------------------------------------------------

drop table tq84_A;