A Treemap is a data visualization technique that displays hierarchical data using nested rectangles. Each rectangle represents a category, and its size corresponds to a specific value, such as sales or population. This method allows users to quickly grasp the relative sizes of different categories and subcategories within a dataset. Treemaps are particularly useful for visualizing large amounts of data in a compact space. They can be applied in various fields, including finance, project management, and web analytics, to help identify patterns, trends, and outliers. Tools like Tableau and D3.js often incorporate treemaps for effective data representation.