Design maneuvering speed is known as:

Maneuvering speed, often referred to as Va, is the maximum speed at which the aircraft can be safely maneuvered without exceeding load limits. It is specifically designed to provide a buffer against stalling during abrupt control inputs. This speed is particularly important in turbulent conditions, hence sometimes called the "rough air speed." At maneuvering speed, the aircraft will stall before it exceeds its structural limits, allowing for better control and safety when encountering turbulence or in defensive maneuvers.

In contrast, the other choices focus on different aspects of flight performance. The maximum operational limit speed relates to the highest permitted speed for safe operation and does not consider the factors that relate to load limits during dynamic maneuvers. Stall speed in a turn refers to the critical speed at which the aircraft will lose lift when turning, but does not account for the dynamic stability that maneuvering speed provides. Lastly, the minimum speed for approach addresses a specific phase of flight concerning landing, which is not directly related to the concept of maneuvering speed and its association with controlling the aircraft in turbulent conditions.