What defines drag in the context of aviation?

In aviation, drag refers to the resistance an aircraft faces as it moves through the air. It is primarily caused by friction and turbulence, which oppose the aircraft's forward motion. As an aircraft travels, air molecules collide with its surface, creating friction, and irregular airflows around the aircraft lead to turbulence. This combination results in a force that acts in the opposite direction to the aircraft's movement, thereby slowing it down.

Understanding drag is crucial for pilots and engineers, as it affects fuel efficiency, speed, and overall aircraft performance. Effective aircraft design aims to minimize drag through streamlined shapes and efficient wing structures, allowing for smoother, faster flight with less energy expenditure.