Scientists define a nut as a kind of fruit with a hard wall around the seed that does not split open when the seed is ripe. The exact part of the plant that becomes the hard shell is part of what separates a true nut from other kinds of fruit. Most people call any seed with a hard shell a nut.
Nutritionally speaking, most nuts and seeds generally contain many of the same nutrients. They’re rich in protein, vitamins, minerals, healthy fats, and fiber.