skip distance

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The smallest separation between a transmitter and a receiver that permits radio signals of a specific frequency to travel from one to the other by reflection from the ionosphere.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the shortest distance that permits radio signals (of a given frequency) to travel from the transmitter to the receiver by reflection from the ionosphere