drop table   test_date;

create table  test_date ( c_date date);

insert into test_date (C_DATE)
values (to_date('01-02-2003', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-04-2004', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-06-2005', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-04-2006', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-09-2006', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-12-2006', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-08-2007', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-11-2007', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-06-2008', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-09-2008', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-11-2008', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-12-2008', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-07-2014', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-07-2005', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-08-2005', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-09-2005', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-09-2007', 'dd-mm-yyyy'));

insert into test_date (C_DATE)
values (to_date('01-10-2007', 'dd-mm-yyyy'));

select  *  from test_date ;

Required out put  :  

Feb ,2013 
Apr , 2014
June,2005 - Sep- 2005
Apr , 2006
Sep, 2006
Dec,2006
Aug 2007 - Nov 2007

select c_date,
       nvl(lead(c_date) over(order by c_date), add_months(c_date, 1)) next_dt,
       case
         when add_months(c_date, 1) =
              nvl(lead(c_date) over(order by c_date), add_months(c_date, 1)) then
         -- row_number() over (order by 1)
         0
         else
         row_number() over (order by 1)
       end val
  from test_date
 order by c_date 

SQL> with 
  2    data as (select distinct trunc(c_date,'MONTH') mnth from test_date),
  3    grouped as (
  4      select mnth,
  5             add_months(mnth,-row_number() over (order by mnth)) grp
  6      from data
  7    )
  8  select to_char(min(mnth),'MM/YYYY') || 
  9           decode(max(mnth),min(mnth),'', '-'||to_char(max(mnth),'MM/YYYY'))
 10           range
 11  from grouped
 12  group by grp
 13  order by grp
 14  /
RANGE
---------------
02/2003
04/2004
06/2005-09/2005
04/2006
09/2006
12/2006
08/2007-11/2007
06/2008
09/2008
11/2008-12/2008
07/2014

select  connect_by_root to_char(c_date,'FMMonth, YYYY') ||
        case when level > 1 then to_char(c_date,' - FMMonth, YYYY') end range
  from  test_date t1
  where connect_by_isleaf = 1
  start with not exists (select 1 from test_date t2 where t2.c_date = add_months(t1.c_date,-1))
  connect by c_date = add_months(prior c_date,1)
  order by c_date
/

RANGE
-------------------------------
February, 2003
April, 2004
June, 2005 - September, 2005
April, 2006
September, 2006
December, 2006
August, 2007 - November, 2007
June, 2008
September, 2008
November, 2008 - December, 2008
July, 2014

11 rows selected.

SQL>