What is Adapter?
A small add-on that lets Astro run server code on a particular host.
Most Astro sites are finished at build time and need no server. When a page has to run code for each visitor, Astro needs to know how your host works, and an adapter teaches it.
Official adapters exist for hosts such as Netlify, Vercel, Cloudflare and Node.js. You only need one if you use on-demand rendering.