SSR, or Server-Side Rendering, is the process of generating the HTML of a web page on the server instead of in the browser. This allows the client to receive fully rendered HTML, improving performance, SEO, and initial load times.
SvelteKit automatically supports SSR by rendering `+page.svelte` and `+layout.svelte` components on the server during the initial request. It also allows hydration on the client so that interactivity is preserved, giving the user a seamless experience.