Domino is a server-side DOM implementation based on Mozilla's Gecko engine. It enables manipulating the DOM outside of a browser environment, useful for tasks like server-side rendering (SSR), web scraping, and testing JavaScript code that relies on the DOM API. It offers a browser-like environment for Node.js, allowing developers to leverage existing DOM manipulation libraries and frameworks on the server. Domino provides a lightweight and efficient way to work with the DOM without requiring a full browser instance.