One of these speeds is what the wings respond to. The other is what a stopwatch and a map respond to. Wind changes the second without touching the first at all.
A pilot flying with a howling 50-knot tailwind watches the ground slide by noticeably faster than usual, arrives early, and burns less fuel per mile of ground covered. It's tempting to describe that as the airplane "flying faster." But nothing about the airplane's actual flight — how hard the wings are working, how close it is to a stall, how the controls feel — has changed at all. That gap, between the speed a stopwatch and a map would measure and the speed the airframe itself actually experiences, is the entire distinction between ground speed and true airspeed.