dead air

(idiomatic, uncountable)An unintended interruption in a broadcast during which nothing is transmitted: a silent period on radio or a silent period with no picture on television.

They fired the production engineer because too many moments of dead air were interrupting the broadcast.

an inadvertent interruption in a broadcast during which there is no sound

(broadly, idiomatic, uncountable)A quiet or awkward moment in a conversation where neither individual is speaking.

Today we're going to try sitting with silence a bit. Don't worry about any moments of dead air in the conversation.

(uncountable)Air that is subject to little or no ventilation, thus, little to no air exchange.