The phenomenon you are describing, where planes appear to be hovering in the sky despite moving forward, is known as "stalling" or "stall." It occurs when an aircraft is flying at a very low airspeed or at a high angle of attack, causing a loss of lift on the wings.
An airplane generates lift through the interaction of its wings with the air. The wings are designed to produce lift by creating a pressure difference between the upper and lower surfaces. When the aircraft is flying at a suitable speed and angle, the airflow over the wings is smooth and generates the necessary lift to keep the plane airborne.
However, if the plane slows down too much or if the angle of the wings relative to the oncoming airflow (angle of attack) becomes too steep, the smooth airflow over the wings becomes disrupted. This disruption leads to a separation of airflow and a decrease in lift production, which can result in a stall.
During a stall, the plane's nose may pitch upward, and the aircraft can appear to hover momentarily or descend abruptly. This is because, without sufficient lift, the aircraft's weight causes it to lose altitude rapidly or remain in a relatively fixed position in the sky.
It's worth noting that when an aircraft is truly hovering, it is usually a result of vertical takeoff and landing capabilities, as seen in helicopters or VTOL (vertical takeoff and landing) aircraft. In these cases, the aircraft has specific design features and propulsion systems that enable it to maintain a stable hover.