The Reddit post in question conflates two distinct aviation concepts, and that conflation itself offers meaningful instructional terrain for working pilots. The so-called "parallax effect" the original poster references — where an aircraft appears stationary in the sky — is more accurately described in aviation safety literature as a collision geometry warning sign: a target aircraft that shows no lateral or vertical movement across the windscreen is likely on a direct collision course, meaning relative bearing is not changing. That concept has nothing to do with ground speed or headwinds, yet the confusion between the two is understandable for a student pilot still building mental models of aerodynamics and spatial awareness simultaneously.
The actual phenomenon the flight instructor was demonstrating is the condition of near-zero or even negative ground speed in a strong headwind — a situation where the aircraft's indicated airspeed remains well above stall while the aircraft makes little or no forward progress over the ground, or in extreme cases appears to drift backward relative to surface references. This is physically possible any time wind speed at altitude approaches or exceeds the aircraft's true airspeed. Light training aircraft such as Cessna 152s or Piper PA-28s with cruise speeds in the 90–110 knot range can encounter this condition in the jet stream or in strong coastal flow regimes. The "funny name" the instructor used was almost certainly something colloquial — "flying backwards," "curtain hover," or similar informal terms used by flight instructors to make the concept memorable — though no single standardized term dominates the training community.
For professional and corporate pilots, the zero or negative ground speed scenario carries operational weight well beyond the novelty of a beach demonstration. Flight planning in high-altitude jet operations routinely requires accounting for jet stream winds that can reduce ground speed by 100 knots or more, dramatically extending flight time, increasing fuel burn, and altering alternate airport calculations. Dispatch and flight crews operating under Part 121 and Part 135 regulations must account for these wind penalties in fuel release calculations, and Part 91 operators flying international or long over-water legs face the same arithmetic. In turboprops and slower business jets operating at lower altitudes in strong surface flow — particularly in mountain wave events or along coastal corridors — unexpectedly low ground speeds can create genuine fuel emergencies if crews anchor to scheduled time-en-route rather than monitoring actual fuel consumption against distance remaining.
The broader instructional value of what this flight instructor was demonstrating touches on one of the more counterintuitive aspects of fixed-wing flight: the complete decoupling of airspeed from ground speed in certain wind conditions. New pilots often carry a car-driver's intuition that speed is a single unified quantity, and early exposure to conditions where the airspeed indicator reads normal while the aircraft sits nearly motionless over a beach is a highly effective corrective. Experienced instructors working in coastal or mountain environments have long used these naturally occurring conditions as teaching moments, and the fact that the student remembered the lesson — even if the name escaped them — suggests the demonstration achieved its purpose. For professional crews transitioning from piston trainers to turbine equipment, this fundamental concept scales directly into the wind planning discipline required for efficient, safe operations across longer ranges and higher altitudes.