Take WordPress and start deleting.

Remove the themes. It still manages content, you just have to render it yourself. Remove the plugin system. Poorer, still a CMS. Remove comments, media handling, multisite, the REST API, the block editor. Keep going until something breaks in a way that means the word no longer applies.

I make it four things.

Somewhere content lives. Files, rows, objects in a bucket. There has to be a durable place, and something has to be authoritative when two copies disagree.

A shape. A blog post has a title, a body, a date. That is a model, even if it is implicit and even if it is only enforced by the form. Without any shape you have a wiki at best and a text editor at worst, because nothing can be reliably queried or listed.

A way in that is not the storage format. Somebody has to be able to change content without editing the storage directly. This is the one that actually defines the category. A directory of HTML files is not a CMS. Add a form that writes those files and it is.

A way out. Rendered pages, an API, a feed, a build artifact. Content that cannot be got back out is an archive, and an archive is a different product.

Everything else that ships in a CMS is a convenience layered on those four. Useful conveniences, some of them load bearing in practice, but a system can lack any of them and still be the thing.

The test is easy to apply and slightly rude, so it is worth applying to the edge cases.

Git plus a static site generator: storage yes, shape yes if there is front matter, way out yes. Way in, no. You edit the storage format directly. Not a CMS, which is not an insult, it is a description of who it is for.

Netlify CMS, or any of the git-backed editors: same storage, same output, but there is now a form that commits for you. That is the whole difference and it is enough. It became a CMS the day it stopped requiring you to know what a commit was.

Google Docs: storage, shape, way in, and a way out if you count export. By this test it is a CMS and nobody calls it one, which tells me the test is necessary but not sufficient. The missing ingredient is intent. A CMS is for content that will be published to an audience under a schedule, and Docs is for documents that will be read by whoever has the link.

Notion sits exactly on that line and has been trying to fall on the CMS side of it for years.

Four parts, then. The next several of these go through them one at a time, starting with storage, because the choice made there constrains every other choice and almost everyone inherits it without deciding.