Definition
The aerodynamic force that acts on an aircraft parallel to and opposite the direction of its flight path through the air, resisting forward motion. Drag is produced by air friction along the aircraft's surfaces and by the production of lift, and it must be overcome by thrust for the aircraft to maintain or increase speed.
Plain English
The pushback the air gives the aircraft as it moves forward. The faster you go or the more lift the wings make, the more the air pushes back against you.
Context Anchor
You will see drag discussed in aircraft performance, climbs, glides, approaches, and any situation where airspeed or power changes matter.
Derivation
From the Old English 'dragan,' meaning to pull or draw along. The aviation use keeps the same idea -- the air is, in effect, pulling backward on the aircraft as it moves through it.
Why Pilots Care
Managing drag directly affects airspeed, fuel consumption, climb performance, and range.
Analogy
Holding your hand flat out of a moving car window creates a strong backward push from the air. That backward push is similar to drag on an aircraft.
Grounding Statement
Picture the resistance felt when holding your arm out the window of a moving car; that push backward is drag acting on the aircraft.
Intuition Check
Drag does not mean something being pulled along the ground here. In aviation, drag means air resistance acting backward against the aircraft’s motion.
Example Sentence 1
Lowering the landing gear added enough drag that the pilot had to add power to hold altitude.
Example Sentence 2
To maintain level cruise the pilot adjusted power so thrust exactly matched drag.