A wind that is blowing opposite your direction of travel... thus resisting your progress in the direction into the wind.

A wind blowing in a direction opposite to the course of a moving object. Often used when referring to winds affecting ballistics.

wind blowing opposite to the path of a ship or aircraft

An adverse wind, usually from the desired direction of travel.

A wind that opposes the intended progress of an exposed, moving object. The opposite of tailwind.

A headwind is a wind that hits an aircraft in the front. This reduces the aircraft's ground speed and increases the time to reach a destination. It is favourable in takeoffs and landings where aviators and Air Traffic Controllers choose the side of the runway with the wind coming against the aircraft.