The article discusses the concept of UI density, which refers to the amount of information an interface can provide over a series of moments. It explores different types of density, including visual density, information density, and design density, and how they relate to user experience. The article also touches on the idea that density is not just about visual elements, but also about the actions a user takes in their journey. The author argues that a good interface should provide the highest value outcomes in the smallest amount of time, space, pixels, and ink.