Density altitude is a measure that combines altitude and atmospheric conditions to indicate air density. It is important for pilots and engineers because lower air density can affect aircraft performance, making it harder for planes to take off and climb. As temperature and humidity increase, density altitude rises, even at lower elevations. To calculate density altitude, one must consider the current air pressure, temperature, and humidity. The higher the density altitude, the thinner the air becomes, which can impact engine performance and lift. Understanding density altitude helps ensure safe operations in aviation and other fields that rely on air density, such as meteorology and aerodynamics.