a sudden and undesirable silence (from the term for the interruption of radio or television broadcasts)
The dead air coming from the bathroom was sign that something dire had happened.
1. An uncomfortable period of awkward silence that usually occurs in a tense social setting;
2. A period of time during which a television show is broadcast without an audio portion.
Man 1: How was the blind date?
Man 2: OK, but we ran out of things to say while we were at the bar. When we sat down for dinner, neither one of us could think of a thing to say. It was 100% dead air for about five minutes.
Man 1: So you didn't get laid?
Man 2: Asshat.