An unmanned free balloon shall refer to a freely drifting inflatable object which is driven with no power, is piloted by nobody, is lighter than air, and whose gross mass is more than 4 kilograms.

• 无人驾驶自由气球，是指无动力驱动、无人操纵、轻于空气、总质量大于4千克自由漂移的充气物体。