TEXT[(M)] [CHARACTER SET charset_name] [COLLATE collation_name]

A TEXT column with a maximum length of 65,535 (216 − 1) characters.
The effective maximum length is less if the value contains multibyte
characters. Each TEXT value is stored using a 2-byte length prefix that
indicates the number of bytes in the value.

An optional length M can be given for this type. If this is done, MySQL
creates the column as the smallest TEXT type large enough to hold
values M characters long.

URL: http://dev.mysql.com/doc/refman/5.7/en/string-type-overview.html

