BLOB[(M)]

A BLOB column with a maximum length of 65,535 (216 - 1) bytes. Each
BLOB 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 BLOB type large enough to hold
values M bytes long.

URL: https://mariadb.com/kb/en/blob/

