dead space

i. An area within the maximum range of a weapon, radar, or observer that cannot be covered by fire or observation from a particular position because of intervening obstacles, the nature of the ground, the characteristics of the trajectory, or the limitations of the pointing capabilities of the weapons.

ii. An area or zone that is within range of a radio transmitter but in which a signal is not received.

iii. The volume of space above and around a gun or guided missile system into which it cannot fire because of mechanical or electronic limitations.

iv. Dead spots in radio-range reception areas over transmitting stations similar to the cone of silence but lacking normal characteristics like buildup, dead spots, surges, and fades. This phenomenon is likely to be caused by flights over mountains, areas of ore deposits, and other factors. See also cone of silence.

v. The area located between the limit of the surface wave and the point of reception of the first sky wave. It is most common in the HF (high frequency) frequency range. Also called the skip zone.