When people talk about the calories in food, what do they mean? A calorie is a unit of measurement—but it doesn't measure weight or length. A calorie is a unit of energy. When you hear something contains 100 calories, it's a way of describing how much energy your body could get from eating or drinking it.

KidsHealth from Nemours, https://kidshealth.org/en/kids/calorie.html ×

This number on a food label indicates how much fat is in a single serving of a food. Limit total fat to less than 25% to 35% percent of the calories you consume each day. All fats have 9 calories per gram.

WebMD, https://www.webmd.com/food-recipes/definitions-glossary

Usually solid at room temperature, saturated fats are found in animal products such as meat and milk, as well as in coconut and palm oil. Saturated fat is often used in foods to prevent rancidity and off flavors. No more than 5% to 10% of your total daily calories should come from saturated fat.

WebMD, https://www.webmd.com/food-recipes/definitions-glossary

While sodium (commonly called salt) is vital for healthy nerves and muscles, most of us get too much salt in our diet, often from processed foods. Read food labels to help keep your sodium intake to 2,300 milligrams a day or less. Persons 51 and older, African Americans, or people who have hypertension, diabetes or chronic kidney disease should limit sodium to 1500 milligrams daily.

WebMD, https://www.webmd.com/food-recipes/definitions-glossary

This number on a food label indicates how many grams of carbohydrates are in a single serving of a food.

WebMD, https://www.webmd.com/food-recipes/definitions-glossary

The part of plant foods that we cannot digest. Whole grains, fruits, vegetables, nuts, and seeds contain fiber. Fiber helps fill you up, can help lower cholesterol, and keeps you regular. You need at least 25 to 38 grams daily. To be considered high in fiber, a food must contain least 5 grams per serving.

WebMD, https://www.webmd.com/food-recipes/definitions-glossary

This section of the nutrition label lists added and natural sugars separately. Added sugars include sucrose, glucose, fructose, and corn and maple syrups. Natural sugars include lactose in milk and fructose in fruit. If you are concerned about your intake of sugar, be sure added sugars are not one of the first few items in a food's ingredients list.

WebMD, https://www.webmd.com/food-recipes/definitions-glossary

Protein in food labeling is the amount of Protein in 100g of the total component. From a nutritional point of view Protein quality labeling is associated with the number and types of amino acid found that can complement the body amino acid requirement and how much of the amino acid in the particular food is appropriate for body protein formation, which is associated with biological value, digestibility, efficiency ratio, and amino acid ration. Protein in nutrition plays a crucial role in almost all biological processes and amino acids are the building blocks of it. A large proportion of our cells, muscles and tissue is made up of amino acids, meaning they carry out many important bodily functions, such as giving cells their structure.

ResearchGate, https://www.researchgate.net/post/What_classifies_protein_in_the_context_of_nutrition_facts_labeling