Radio silence is a deliberate cessation of communications, typically for the duration of some sensitive time period.
Radio silence may be mandated or voluntary. Strictly speaking, the term refers to the transmissions of radio stations, which in this context include anything capable of sending our a radio signal. The term has both military and civilian applications and is also used metaphorically in a variety of contexts.
Examples of radio silence:
In the military, radio transmissions may be forbidden as a means of preventing discovery of sensitive information, such as the location of a troop.
In nautical and aviation emergency situations, radio silence may be mandated to avoid interference that makes it harder to detect a distress signal.
Prior to the release of a product, a manufacturer might enforce a ban on discussing it for a variety of reasons, such as protecting information from competitive intelligence efforts and increasing speculative buzz in the marketplace.
In casual usage, people often use radio silence to refer to any situation in which other people deliberately stop communicating or fail to respond. Common examples of radio silence include text exchanges and chats in which one person stops answering and Facebook posts or tweets that fail to generate the anticipated level of responses.