The Sitecore JSS Next.js website is served through multiple Azure functions. The jss-nextjs-app-azure-functions package contains these functions.
jss-nextjs-server - The actual Next.js web server, including Incremental Static Regeneration.
jss-exp-editor-render - A function to handle the render calls from the Sitecore Experience Editor.
jss-exp-editor-data - A function to handle the data calls from the Sitecore Experience Editor.