What are the posts in the “References” category?

These are posts referred to in some way from elsewhere in the blog. I put them here to reduce clutter.
Since each post in this category is (at least in principle) linked to by some other post, I have set this category so it does not display on the front page.
This post is the exception; nothing links to it. If you are reading this, you already know how to get to the “References” archive.