What is hydration?

Hydration is the process of restoring interactivity on the client after the server has rendered the HTML page.

In modern frameworks (such as React, Vue), the server first generates static HTML, which is quickly displayed in the browser. Then JavaScript is loaded on the client, which "hydrates" this HTML, i.e., connects it with the application's logic and state, making the page interactive.

Example: the server delivers ready-made HTML with button markup, and after hydration, the button becomes clickable and responds to events.