The Virtual DOM (Document Object Model) is a concept used in web development frameworks like React.js to optimize the performance of web applications. It's a virtual representation of the DOM tree, which is a hierarchical representation of HTML elements in a web page.

Here's how the Virtual DOM works:

1. Virtual DOM Creation: When changes are made to the data or state of a web application (for example, when a user interacts with the interface), React.js creates a new virtual DOM tree that reflects these changes. This virtual DOM tree is a lightweight, in-memory representation of the actual DOM.

2. Difference Calculation: After the virtual DOM is updated, React.js compares it with the previous virtual DOM (created before the change). It calculates the differences, or "diffs," between the two virtual DOM trees to determine which parts of the actual DOM need to be updated.

3. Minimal DOM Updates: Instead of directly updating the entire DOM, React.js identifies only the specific elements that have changed based on the calculated differences. It then updates these elements in the actual DOM, minimizing the number of DOM manipulations required.

4. Batched Updates: React.js may batch multiple updates together and perform them in a single pass to further optimize performance. This reduces the overhead associated with frequent DOM updates and enhances the responsiveness of the web application.

By using the Virtual DOM, React.js and similar frameworks can achieve faster rendering performance and better overall efficiency compared to directly manipulating the actual DOM. This approach allows developers to create dynamic and interactive web applications with smoother user experiences.