> 3. Actions

It is somewhat explained as a convention or something built-in, but I can't find much about it elsewhere. Is it the author's own convention or am I missing something?

Yeah, I wondered about that too as normally Django "actions" mean admin actions (https://docs.djangoproject.com/en/dev/ref/contrib/admin/acti...). But in this case it seems the blog post is referring to this pattern: https://www.jmduke.com/posts/in-praise-of-actions.html (same author)