sql - MySQL database table creation -

in mysql database, table has been created follows:

create table if not exists `sub` ( `s_id` int(3) not null auto_increment comment 'standard id', `std` int(10) not null comment 'standard', `sub_nm` varchar(25) not null comment 'subject name',  primary key (`s_id`),  key `sub_nm` (`sub_nm`),  key `sub_nm_2` (`sub_nm`),  key `sub_nm_3` (`sub_nm`)  )    engine=innodb  default charset=latin1 comment='all subjects      corresponding standerds.' auto_increment=21 ; 

my question is, meant last 3 key values? mean: key sub_nm (sub_nm), key sub_nm_2 (sub_nm), , key sub_nm_3 (sub_nm)

with instruction key sub_nm (sub_nm), key sub_nm_2 (sub_nm), key sub_nm_3 (sub_nm) create 3 indexes sub_nm column named sun_nm, sub_nm_2 , sub_nm_3