A wind that is blowing in your direction of travel... thus enhancing your progress in the direction of wind.

wind blowing in the same direction as the path of a ship or aircraft

A wind which assists the intended progress of an exposed, moving object, rendering the objects groundspeed greater than its airspeed.

(Also called following wind wind that assists the intended progress of an exposed, moving object, for example, rendering an airborne object's groundspeed greater than its airspeed; the opposite of a headwind. The tailwind component is directed along the heading, not the course. See wind factor, crosswind.

A tailwind is a wind that hits an aircraft from behind. This reduces the flight time by increasing the ground speed. Tailwind is an unfavorable characteristic when taking off or landing and is usually countered by landing in the direction of the runway.