Data density refers to the amount of information contained within a given space or area. It is often measured in terms of how many data points or values are represented in a specific unit, such as a square inch or a pixel. High data density means that a lot of information is packed into a small area, while low data density indicates that information is spread out over a larger space. In the context of data visualization, charts and graphs with high data density can convey more information at a glance, but they may also become cluttered and difficult to interpret. Conversely, low data density visualizations are easier to read but may oversimplify the data, potentially omitting important details.