ENUM('value1','value2',...) [CHARACTER SET charset_name] [COLLATE
collation_name]

An enumeration. A string object that can have only one value, chosen
from the list of values 'value1', 'value2', ..., NULL or the special ''
error value. ENUM values are represented internally as integers.

An ENUM column can have a maximum of 65,535 distinct elements. (The
practical limit is less than 3000.) A table can have no more than 255
unique element list definitions among its ENUM and SET columns
considered as a group. For more information on these limits, see
http://dev.mysql.com/doc/refman/5.5/en/limits-frm-file.html.

URL: http://dev.mysql.com/doc/refman/5.5/en/string-type-overview.html

