Nutrient density is the measure of the amount of beneficial nutrients in a food product in proportion to it's energy content, weight or amount of detrimental nutrients. It is a way of evaluating the nutritional quality of a food by comparing the amount of nutrients consumed in a bite a meal or day.
A 'nutrient dense' food supplies significant amounts of one or more nutrients compared to the number of calories it has. Eggs, for example, have a high nutrient density, because they provide protein and many vitamins and minerals in proportion their calories. So an egg is considered to be 'nutrient dense'
Nutrient Density in Action
Examples from around the world
Pan American Health Organization
"The purpose of nutrient profiling is to provide a tool to classify food and drink products that are in excess of free sugars, salt, total fat, saturated fat and trans-fatty acids."