Server-side rendering (SSR) is a technique used in web development to improve the performance and SEO of web applications. In the context of Next.js, SSR refers to the process of rendering React components on the server side before sending the fully-rendered HTML to the client's browser. This approach has several advantages over traditional client-side rendering (CSR), where the rendering process occurs on the client's device.
Here's how server-side rendering works in Next.js:
- User Requests a Page: When a user requests a page of your Next.js application by entering a URL or clicking a link, the server receives the request.
 - Server-side Rendering: In a Next.js application configured for SSR, the server renders the requested page on the server side. This involves executing the relevant React components for the requested page and generating the HTML content that represents the page's initial state.
 - HTML Response: Once the rendering process is complete, the server sends the fully-rendered HTML content to the client's browser as a response to the user's request. This HTML content includes the initial data and UI of the requested page.
 - Client Hydration: When the browser receives the HTML content, it also downloads the necessary JavaScript bundles that contain the React components and logic. The JavaScript code takes over the interactivity of the page, attaching event listeners, handling user interactions, and managing dynamic updates.
 - Interactivity and Routing: From this point on, the application behaves like a traditional React application, handling client-side routing, state management, and dynamic updates as users interact with the page.