Dead air is defined as "a period of silence especially during a radio broadcast," which has been extended, in some formal definitions, to include both audio and video signals (and so to this extent, to television as well as radio broadcasts). Hence, generalizing, the term can be understood to refer to any unintended period of silence interrupting any media broadcast, during which no signal, audio or video, is transmitted. Technically, the absence of sound in a radio transmission implies that only an unmodulated carrier wave is being transmitted, for modes that send one, or absence of the transmitting signal altogether for modes that do not.
The term is most often used in cases where program material comes to an unexpected halt, either through operator error or for technical reasons. Among professional broadcasters, dead air is considered one of the worst things that can occur. Moreover, dead air could affect advertising revenue if it affects the airplay of paid commercials.
As noted, the term "dead air" is also sometimes used in television broadcasting, generally when a television channel has an interruption to its output, resulting in a blank screen or in the case of digital television, a frozen image, until output is restored or an apology message is broadcast.
Some television stations also use the related phrases "in black" and "going to black" for transmitting an unmodulated carrier, meaning both a completely black image and a completely silent audio stream are sent; other stations limit the term "in black" to loss of video where audio continues normally, and "dead air" is used for sending an unmodulated carrier signal.
Television directors use the command "fade to black" or "to black" to indicate a transition to a completely black image.
However, the terms "dead air" and "in black" are not used when a station is broadcasting no signal whatsoever, even a carrier wave, which is called "going off-the-air."
An example of dead air was a Chris Evans radio transmission for the British Virgin Radio (now known as Absolute Radio) station. As a promotional stunt, Evans did not arrive for work, "forcing Vanessa Feltz to fill the dead air with jokes".
On September 11, 1987, Dan Rather walked off the set of the CBS Evening News when a late running U.S. Open tennis match threatened to delay the start of his news broadcast. The match then ended sooner than expected but Rather was gone. The network broadcast six minutes of dead air before Rather was found and returned to the studio. CBS affiliates criticized Rather for the incident.
One significant case of dead air occurred during Super Bowl LII in 2018, when the NBC television broadcast experienced 26 seconds of dead air during a commercial break. The network blamed "a brief equipment failure", and stated that no commercial advertising was lost. Prior to Super Bowl XLV, Green Bay radio station WCHK-FM announced that it would intentionally go to dead air during the game, since the hometown Packers were playing in the game.