The term "Pitch Angle" refers to the angle between the horizontal plane and the line of an object, such as an aircraft or a propeller blade, when it is tilted forward or backward. This angle is crucial in aerodynamics, as it affects lift and drag, influencing how well an aircraft can ascend or descend. In the context of helicopters, the pitch angle of the rotor blades can be adjusted to control the amount of lift generated. A higher pitch angle increases lift but also increases drag, while a lower pitch angle decreases lift and drag, allowing for more efficient flight.