Syntax:
CURRENT_USER, CURRENT_USER()

Returns the username and hostname combination for the MySQL account
that the server used to authenticate the current client. This account
determines your access privileges. As of MySQL 5.0.10, within a stored
routine that is defined with the SQL SECURITY DEFINER characteristic,
CURRENT_USER() returns the creator of the routine. The return value is
a string in the utf8 character set.

The value of CURRENT_USER() can differ from the value of USER().

URL: http://dev.mysql.com/doc/refman/5.0/en/information-functions.html

