Meaning of horizon distance

hori'zon dis"tance

Pronunciation: [key]
  1. the distance of the farthest point on the earth's surface visible from a transmitting antenna.
  2. the distance on the earth's surface reached by a direct wave: due to atmospheric refraction, sometimes greater than the distance to the visible horizon.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.