Partial pressure refers to the pressure exerted by a single gas in a mixture of gases. It is a way to understand how each gas contributes to the total pressure of the mixture. For example, in a container filled with air, the oxygen and nitrogen each have their own partial pressures, which together add up to the total atmospheric pressure. The concept of partial pressure is important in various fields, including chemistry, biology, and engineering. It helps explain phenomena such as gas exchange in the lungs, where the partial pressures of oxygen and carbon dioxide determine how gases move between the blood and the air.