What a content type actually is

A content type is a promise about shape. Every entry of that type has the same fields, so anything consuming it can rely on them being there.

Start from the consumer

Ask what a page, a feed, and an app screen each need from this thing. The fields they agree on are the content type. The rest is either presentation or a different type wearing a disguise.

A worked example

A blog post has a title, a body, an author and a date. It does not have a hero image alignment, a background colour, or a "show sidebar" toggle. Those are decisions the renderer makes, and freezing them into entries is how content stops being portable.