Create table mysql

Hello all,

I'am new to mysql and i want to know what KEY (not primary key) means in the query below :

    CREATE TABLE `users` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) NOT NULL default '',
  `username` varchar(150) NOT NULL default '',
  `email` varchar(100) NOT NULL default '',
  `password` varchar(100) NOT NULL default '',
  `activation` varchar(100) NOT NULL default '',
  PRIMARY KEY  (`id`),
  KEY `idx_name` (`name`),
  KEY `username` (`username`),
  KEY `email` (`email`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=65 ;

also this line ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=65 ;