Mach Tuck is an aerodynamic phenomenon that occurs when the aircraft reaches a defined supersonic speed, generally ranging between 0.75 mach to 1.25 mach. This phenomenon involves the aircraft’s nose pitching down at the same time when the airflow around the wings reaches or surpasses the critical Mach number.
The aircraft’s tendency to dive under can also be called Tuck Diving and can be corrected by reducing the aircraft’s speed or adjusting the aircraft’s design to prevent disruption in the airflow. 

BY Best Interview Question ON 11 Oct 2023