Syntax:
DROP USER user [, user] ...

The DROP USER statement removes one or more MySQL accounts and their
privileges. It removes privilege rows for the account from all grant
tables. To use this statement, you must have the global CREATE USER
privilege or the DELETE privilege for the mysql database. Each account
name uses the format described in
http://dev.mysql.com/doc/refman/5.5/en/account-names.html. For example:

DROP USER 'jeffrey'@'localhost';

If you specify only the user name part of the account name, a host name
part of '%' is used.

URL: http://dev.mysql.com/doc/refman/5.5/en/drop-user.html

