As you already learned, there are some reserved filenames when working with NextJS.

Important: These filenames are only reserved when creating them inside of the app/ folder (or any subfolder). Outside of the app/ folder, these filenames are not treated in any special way.

Here's a list of reserved filenames in NextJS - you'll, of course, learn about the important ones throughout this section:

• page.js => Create a new page (e.g., app/about/page.js creates a <your-domain>/about page)

• layout.js => Create a new layout that wraps sibling and nested pages

• not-found.js => Fallback page for "Not Found" errors (thrown by sibling or nested pages or layouts)

• error.js => Fallback page for other errors (thrown by sibling pages or nested pages or layouts)

• loading.js => Fallback page which is shown whilst sibling or nested pages (or layouts) are fetching data

• route.js => Allows you to create an API route (i.e., a page which does NOT return JSX code but instead data, e.g., in the JSON format)

You also find a list with all supported filenames & detailed explanations in the official docs: https://nextjs.org/docs/app/api-reference/file-conventions