Syntax:
{EXPLAIN | DESCRIBE | DESC}
    tbl_name [col_name | wild]

{EXPLAIN | DESCRIBE | DESC}
    [explain_type] SELECT select_options

explain_type: {EXTENDED | PARTITIONS}

The DESCRIBE and EXPLAIN statements are synonyms. In practice, the
DESCRIBE keyword is more often used to obtain information about table
structure, whereas EXPLAIN is used to obtain a query execution plan
(that is, an explanation of how MySQL would execute a query).

URL: http://dev.mysql.com/doc/refman/5.5/en/explain.html

