What is the best definition for a nutrient?

A nutrient is a substance that provides essential nourishment for growth, metabolism, and overall health in living organisms. Nutrients are classified into macronutrients, such as carbohydrates, proteins, and fats, which are needed in larger amounts, and micronutrients, such as vitamins and minerals, which are required in smaller quantities. They play crucial roles in various bodily functions, including energy production, immune response, and tissue repair.