Definition
The normal airflow around a wing in flight, in which air moves not only over and under the wing from front to back, but also spanwise (sideways along the wing) and around the wingtips, where higher-pressure air below curls up to meet lower-pressure air above. This spanwise and tip movement creates wingtip vortices and induced downwash behind the wing.
Plain English
When a wing produces lift, air doesn't just flow straight back over it. It also slips sideways along the wing and curls around the tips, which creates spinning air behind each wingtip and pushes air downward behind the wing.
Context Anchor
Seen in ground effect discussions, especially when explaining why an airplane may feel like it floats close to the runway during landing or lift off more easily during takeoff.
Derivation
Three-dimensional means the airflow has motion in all three directions -- forward/backward, up/down, and side-to-side. A simple two-dimensional view of a wing only shows air going over and under it; calling the real flow 'three-dimensional' reminds us the sideways and tip movements matter too.
Why Pilots Care
Recognizing this flow explains why induced drag drops close to the ground, allowing shorter takeoffs and softer landings.
Grounding Statement
Picture air flowing over a wing in flight: most goes straight back, but some slides sideways toward the tips and spirals off the wingtips into rotating cones of air trailing behind the airplane.
Intuition Check
Do not read this as simply a 3-D drawing or diagram. Here it means the real air around the wing is moving in three directions, and the ground changes that movement.
Example Sentence 1
Out of ground effect, the wing produces a full three-dimensional flow pattern, complete with wingtip vortices and induced downwash.
Example Sentence 2
As the airplane enters ground effect, the three-dimensional flow pattern changes and induced drag decreases.