What is a calorie?

A calorie is defined as a measure of energy, specifically the amount of energy required to raise the temperature of one gram of water by one degree Celsius at standard atmospheric pressure. This unit is commonly used in the fields of nutrition and physics to quantify energy expenditure and transfer. It plays a crucial role in understanding the energy content of foods and the energy required for physical activities.

In the context of the other options, pressure is measured in units such as pascals or atmospheres, temperature is measured in Celsius, Fahrenheit, or Kelvin, and force is measured in newtons. These definitions are distinct and do not relate to the concept of calories as a measure of energy.