A calorie is a measure of energy. In scientific terms, a calorie is the amount of energy needed to increase the temperature of 1 kilogram of water by 1°C. Thus, the more calories a food contains, the more energy it supplies to your body. A calorie isn’t “good” or “bad”—it just is. Different foods will offer more nutritional benefits than others, but ultimately a calorie is still a calorie and nothing more than a measure of energy.
If you have a very active lifestyle, your body will use or “burn” a greater number of calories to function every day. Activities that make you feel physically tired, like running, playing sports, yard work, or significant walking, will burn more calories than sitting around doing nothing.