The term "nutritional powerhouse" is used to describe foods that are exceptionally rich in essential nutrients, vitamins and minerals. These types of foods provide a high level of health benefits due to their dense concentration of important nutrients that our bodies need to function properly. They often contain antioxidants, fiber, protein, and other vital components that help maintain good overall health. In summary, the phrase "nutritional powerhouse" refers to foods with exceptional nutritive value that can significantly improve one's diet and well-being.