In a CREATE TABLE statment, why "KEY" is used in this way? KEY `IDX_ATTRIBUTE_LABEL_ATTRIBUTE` (`attribute_id`)

I'm trying to understand this table structure. I never seen this kind of statement, is this some kind of foreign key?

there's n开发者_运维问答o table like *IDX_ATTRIBUTE_LABEL_ATTRIBUTE*

CREATE TABLE IF NOT EXISTS `eav_attribute_label (
  `attribute_label_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `attribute_id` smallint(5) unsigned NOT NULL DEFAULT '0',
  `store_id` smallint(5) unsigned NOT NULL DEFAULT '0',
  `value` varchar(255) NOT NULL DEFAULT '',
  PRIMARY KEY (`attribute_label_id`),
  KEY `IDX_ATTRIBUTE_LABEL_ATTRIBUTE` (`attribute_id`),
  KEY `IDX_ATTRIBUTE_LABEL_STORE` (`store_id`),
  KEY `IDX_ATTRIBUTE_LABEL_ATTRIBUTE_STORE` (`attribute_id`,`store_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=2 ;

thanks

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In this case KEY is a synonym for INDEX, it is not a foreign key.

Note - index on attribute_id is redundant because there is composite index (attribute_id,store_id).