OK, based on your link the answer to my question seems to be: it's not a tracking pixel, but the "Meta Pixel", which the documentation describes as "a snippet of JavaScript code".
Welcome to the wonderful world of affiliate marketing, adtech, and tag management.
In that world, third party ‘tags’ that are included in a page are generally referred to as ‘pixels’. Sometimes they are single pixel img tags. Frequently they are scripts. But the industry calls them ‘pixels’ anyway.
It is, surprisingly, not a terribly honest industry.
I don't know why you're being downvoted, calling full access javascript embedded into a page a 'tracking pixel' is a total lie. Then again 'serverless' is where you use a server, so the track record isn't great.
I guess most people reading this already knew that the term 'tracking pixel' has evolved beyond its original meaning, and is now commonly understood to include all sorts of tracking code.
I did not, but now I know :)
(And although serverless doesn't mean 'no server', we know what the word means and it doesn't cause confusion.)
In that world, third party ‘tags’ that are included in a page are generally referred to as ‘pixels’. Sometimes they are single pixel img tags. Frequently they are scripts. But the industry calls them ‘pixels’ anyway.
It is, surprisingly, not a terribly honest industry.