As joeriel pointed out, MFA stands for "Made For AdSense".
To elaborate just a bit, these are web sites whose sole purpose for existing is to display ads. Instead of the "traditional route" where site owners decide to show ads on their existing sites to generate a few bucks of revenue, somebody sat down and started coming up with a list of ideas or topics for web sites to create just to display ads. Think "we need some ads on the site" versus "we need some content to wrap around the ads".
If you've ever gotten a phone call from an unknown number and typed it into Google in an attempt to find out who was calling, well, you almost certainly found several examples of these sites right there on the first page of the results.
These sites are usually low-quality and light on the content -- which is very often just some existing data they've found (e.g., gathered from public datasets or scraped from somewhere else) and dumped into an SQL database in order to generate 100s or 1000s of "dynamic" pages. Many times they're based on some "long tail" search terms/keywords.
There are exceptions, of course, but I think you get the point. Personally, I hate these types of web sites; there's enough "shit" on the Internet already.
I believe it stands for Marketing Funnel Automation. Basically sites that suck people in and point them to an affiliate link to earn a little bit. Could be wrong.
https://flippa.com/
It's probably a good idea to learn from what worked for them/what they iterated to as well