The phrase “GNU Terry Pratchett” originates from one of the Discworld novels, “Going Postal,” where it is used as a code or message passed between characters to remember the deceased.
Specifically, there is a communication system known as “the clacks”, and there part of the way that system works involves additional metadata messages being sent (known as “the overhead”).
I only recently discovered that people have been embedding that message in all sorts of things as a way to memorialize Terry. One of the places they do this in the headers of websites.
So, you will now see an additional header in all the HTTP responses on this site:
X-Clacks-Overhead: GNU Terry Pratchett