Skip zone is:

The 'skip zone' (sometimes called the dead zone) is the geographical area where you cannot hear a specific transmitting station. It begins at the exact point where the transmitter's ground wave becomes too weak to hear, and it ends at the point where the first skywave successfully refracts back down to Earth. Many learners confuse this with the distance from the antenna itself. However, because the ground wave covers the immediate area around the transmitting antenna, that close-in area is not 'skipped'. The zone of silence only starts after the ground wave dies out. Distractors mentioning 'lost sky waves' or the space 'between any two refracted waves' do not accurately describe the skip zone, which is specifically the gap between local ground wave coverage and distant skywave coverage.