What is meant by the term "ground effect" in aviation?

The term "ground effect" refers to a phenomenon that occurs when an aircraft is flying close to the ground, typically within one wingspan's distance from the surface. As the aircraft approaches this altitude, the airflow around the wings is altered due to the proximity of the ground. This alteration results in an increase in lift and a decrease in drag, allowing the aircraft to maintain a given speed with less power compared to when it is further away from the ground.

Ground effect is especially pronounced during takeoff and landing phases of flight. When an aircraft is near the ground, the high-pressure air beneath the wings compresses, which can enhance lift, making it easier to become airborne. Similarly, during landing, pilots may encounter a "floating" sensation as they descend due to the increased lift generated by the ground effect.

Other factors outlined in the options do not accurately depict ground effect. While increased drag and reduced control might occur in other circumstances, they do not represent the benefits of ground effect. Reduced visibility is also not related to the ground effect but pertains to other flying conditions. Lastly, a decrease in engine efficiency at lower altitudes describes how engine performance can change with altitude but is unrelated to the lift and drag characteristics defined by ground effect.