On-the-air

In telecommunication, the term on-the-air has the following meanings:

1. In radio communications systems, pertaining to a station that is transmitting a carrier, whether or not the carrier is modulated.

2. In a radio station, pertaining to a particular source of modulation, such as a specific microphone, that is connected, i.e., is capable of modulating the carrier.

Source: from Federal Standard 1037C