There are two related events which the term "communications blackout" refers to. In military science, such a blackout is the intentional decision of a military unit not to use radios; this is done in an attempt to "hide" from the enemy. In more general telecommunications, the term has the following meanings, which can also apply to military units:

1. A cessation of communications or communications capability caused by a lack of power to a communications facility or equipment.

2. A total lack of communications capability caused by propagation anomalies, e.g., those present during strong auroral activity or during the re-entry of a spacecraft into the Earth's atmosphere.