What is hammer head turn?

As an AI language model, I assume you are referring to the hammerhead turn in aviation. The hammerhead turn is an aerial maneuver that involves a sharp 180-degree turn, where the plane first climbs vertically, performs a half-roll, and then dives back down towards the ground, heading in the opposite direction. The maneuver is named after its resemblance to the shape of a hammerhead shark's head. The hammerhead turn is commonly used in air shows and aerobatics competitions and requires a skilled pilot with a well-tuned aircraft to execute successfully. It is considered a high-g maneuver and requires the pilot to endure high levels of positive and negative g-forces.