the deviation (by a vessel or aircraft) from its intended course due to drifting
driftage详细解释
drift.age n.（名词）Deviation from a set course caused by drifting.偏移：由于漂动而从既定路线上偏离Matter that has been carried along or deposited by air or water currents.漂流物：被气流或水流携带或沉积的物体
