What does "autodidact" mean?

There is a unity to coherently tamed things, which comes from their tamer. If feral things have any unity, it comes from commonalities in the world itself that they all are forced to hew to because the world they autonomously explore itself contains regularities.

I don't think this is always true, rather it depends on how uniform the applications are, and how accessible they are. Sometimes autodidacts teach themselves in an ivory-tower setting, whereas allodidacts at least has an ivory tower that has a social network guiding it somewhat towards practical tasks.

But then somehow, in the course of becoming a tenured professor of statistics, he ended up saying stuff like "iq is a statistical myth" as if he were some kind of normy, and afraid of the big bad wolf? (At least he did it in an interesting way... I disagree with his conclusions but learned from his long and detailed justification.)

I'd be curious if you have any good arguments for your disagreement. At least you seem to be thinking that IQ tests measure intelligence, which is a stronger assertion than I'd make.

However, nowhere in that essay does he follow up the claim with any kind of logical sociological consequences. Once you've become so nihilistic about the metaphysical reality of measurable things as to deny that "intelligence is a thing", wouldn't the intellectually honest thing be to follow that up with a call to disband all social psychology departments? They are, after all, very methodologically derivative of (and even more clearly fake than) the idea, and the purveyors of the idea, that "human intelligence" is "a thing". If you say "intelligence" isn't real, then what the hell kind of ontic status (or research funding) does "grit" deserve???

Intelligence and grit are differential psychology rather than social psychology. Social psychology tends to focus more on interventions (but also tends to have an order of magnitude lower sample sizes, hence replication crisis), addressing some of the objections that Cosma Shalizi raised.

These days, professional exams have been largely subsumed by university degrees, but there used to be people who'd just study on their own for a bar exam, highway engineer exam, actuarial exam, etc, and then go work in that field. How would that fit into your classification?

No, it’s just a sense of the word I’m familiar with. But I find that googling “mere autodidact” gives a wealth of examples.

I suspect this may actually be the most important thing the educational system does.

You can learn from books or online videos. You can find fellow learners on social networks. You can find motivation... at random places.

But without being shown a direction, you will probably get lost in a sea of nonsense. A simple advice, such as "chemistry is the thing you should study, not alchemy" can save you decades of time you might otherwise waste learning useless things.

It is easy to notice the damage school system does, and easy to take its benefits for granted. Even if you are homeschooled, you are still exposed to people who got the right directions. (People from crazy religious families may be prevented from getting the right direction in e.g. biology or sex education, but they will still probably get the right directions about math or chemistry or geography.) This did not happen spontaneously. It was the educational system that redirected billions of people from thinking about superstitions and magic and astrology and homeopathy and whatever else, towards thinking about math and physics and chemistry and geography and history. Even if for many people the success is only partial, the fact that they even know about the useful stuff means a lot.

In today's world, you can become good at math without spending a single day at school. But in a world where everyone in the last three generations was an autodidact, you most likely wouldn't be good at math, because you most likely wouldn't even know that there was such a thing as math. (Unless you would be lucky to be born in a family of mathematicians.) Instead you would spend your time learning... some nonsense. Some difficult nonsense that requires high IQ and lot of studying to get it impressively right. Just like Newton spent half of his life doing astrology.

Autodidacts are easily recognized by their unknown unknowns. They may know a lot, but what they don't know, they usually don't even know that it exists.