What does “autodidact” mean?

Alice takes a chemistry class at a university. She gets a professor who basically just reads from the textbook during lectures. She reads the textbook on her own, talks to her classmates, and finds some relevant Wikipedia articles and youtube videos.

Bob studies chemistry on his own. He buys the textbook Alice uses because it’s popular, reads it on his own, talks to other people interested in chemistry, and finds some relevant Wikipedia articles and youtube videos.

Bob is an autodidact. Alice is not.

OK, I understand that, but what’s the key difference? What is the essence of autodidact-ness? Is it...

  • The mere involvement of a “legitimate” institution, even if it makes no real difference to the individual’s learning experience?

  • Some essential difference in the experience that Alice and Bob have while learning?

  • Something different about the personal character of Alice and Bob?

I don’t think there’s a clear consensus, and I don’t think it describes a clear distinction, and that’s why I don’t normally use the word “autodidact”.