multi-column index

What is multiple-column index? MySQL or many RDBMS supports multiple-column indexes. i.e. The index key will be more than 1 column in the table. For example, consider a table consolidated CREATE TABLE `consolidated` ( `consolidated_id` int(11) NOT NULL AUTO_INCREMENT, `pub_id` int(11) DEFAULT NULL, `cp_id` int(11) DEFAULT NULL, `ro_id` int(11) DEFAULT NULL, `country_id` int(11) DEFAULT NULL, […]