The tag is present in Lintian version 2.104.234. That is the most recent version we know about.
One or more lines in the extended part of the "Description:" field have been found to contain more than 80 characters. For the benefit of users of 80x25 terminals, it is recommended that the lines do not exceed 80 characters.
Refer to Debian Policy Manual section 3.4.1 for details.