mySQL's KEY keyword?

Question

CREATE TABLE groups ( ug_main_grp_id smallint NOT NULL default '0', ug_uid smallint default NULL, ug_grp_id smallint default NULL, KEY (ug_main_grp_id) );

What does the KEY keyword mean? It's not a primary key, its not a foriegn key, so is it just an index? If so, whats so special about this type of index created with KEY? Sorry if I'm all over the place heh

Answer 1

Quoting from http://dev.mysql.com/doc/refman/5.1/en/create-table.html

{INDEX|KEY}

So KEY is an INDEX ;)