Static sites are not to be confused with decoupled (headless) sites.
Decoupled sites get their name from the fact that their user-facing front-end is separated from the back-end system where the content is managed and stored.
This separation - in theory - offers two main advantages:
- a single mechanism to deliver content to different channels (devices)
- switch from one CMS to another without having to (significantly) rewrite the front-end
A decoupled site's front-end is kind of like a fully designed but mostly empty shell that uses JavaScript to communicate with a server to fetch all of its content and navigation menus in bits and pieces (chunks). These chunks are either (re)generated in real-time, or pre-rendered and cached for performance reasons.
Since the front-end only consists of HTML, CSS, Javascript, and other static assets, it can be hosted by any provider that offers static hosting. But it can not function without its content management back-end that must be hosted elsewhere.
Decoupled sites still rely on a CMS like Drupal, while static sites are self-contained. As a result decoupled sites can offer more interactivity and/or dynamic features than static sites, but decoupled sites still need a CMS running on a server somewhere.
Examples of Decoupled Drupal solutions: