BIT[(M)]

A bit-field type. M indicates the number of bits per value, from 1 to
64. The default is 1 if M is omitted.

This data type was added in MySQL 5.0.3 for MyISAM, and extended in
5.0.5 to MEMORY, InnoDB, and BDB. Before 5.0.3, BIT is a synonym for
TINYINT(1).

URL: http://dev.mysql.com/doc/refman/5.0/en/numeric-type-overview.html

