Difference between "prerender" in root layout and "adapter-static"?

[MikeMcDonald83]

I'm making a static site that can be built from external documents and Svelte components. It will be hosted on GitHub Pages. In the tutorial for SvelteKit page options, it says,

Setting prerender to true inside your root +layout.server.js effectively turns SvelteKit into a static site generator (SSG).

In the reference (which I found by Googling "sveltekit ssg") it says to use the adapter-static adapter for SSG. I'm not saying these are contradictory. I am just wondering what the difference is. For example, do the two options affect CSR plumbing in different ways? Does the adapter do stricter tests? Is it bad practice to skip the adapter?

Somewhat relatedly, the adapter-static readme says,

If you'd like to prerender only some pages and dynamically server-render others, you will need to use a different adapter together with prerender.

What is meant by "different adapter"? Does that include no adapter? Does that include the default adapter, if such a thing exists? The ambiguity is a little confusing, like you might need a specific unnamed adapter.

Thanks!