Definition
The drag produced by an aircraft moving through the air that is not associated with the production of lift. It includes form drag (caused by the shape of the aircraft pushing air aside), skin friction drag (caused by air rubbing along the aircraft's surfaces), and interference drag (caused by air currents from different parts of the aircraft mixing together). Parasite drag increases as airspeed increases, roughly with the square of the speed.
Plain English
It's the drag the airplane creates simply by pushing through the air. The faster you fly, the more of it there is. It has nothing to do with making lift -- it's just the air resisting the airplane's shape, surfaces, and joints.
Context Anchor
Seen in takeoff and ground effect discussions, especially when comparing drag that decreases near the ground with drag that still increases as the airplane speeds up.
Derivation
Parasite' comes from the Greek 'parasitos,' meaning something that takes without giving back. The name fits because this drag costs the airplane energy without contributing anything useful -- unlike induced drag, which is the unavoidable cost of producing lift.
Why Pilots Care
Parasite drag rises sharply with speed and becomes the dominant drag factor at high velocities, directly limiting maximum cruise speed and increasing fuel burn.
Grounding Statement
As the airplane speeds up, more air hits and rubs over the airplane each second, so parasite drag increases.
Intuition Check
“Parasite” does not mean anything biological here. It means drag that comes along with moving the airplane through the air but does not help produce lift.
Example Sentence 1
Lowering the landing gear adds parasite drag, which is why the airplane slows noticeably after gear extension.
Example Sentence 2
Reducing the size of antennas lowered parasite drag and improved fuel economy on long flights.