What does Push-to-Talk (PTT) mean?
Push-to-talk (PTT or P2T) is a method of telecommunications that normally uses a half duplex system. As the name implies, Push To Talk (PTT) requires the person talking to press a button for the other party at the other end of the line to hear him. Because basic PTT uses half duplex, only one person can talk at a time. Police radios, air traffic controller telecommunications systems, and even some cellular technologies (e.g. iDEN) employ Push To Talk.
Techopedia explains Push-to-Talk (PTT)
PTT users communicate bidirectionally but not simultaneously during voice transmission, i.e., callers take turns speaking and listening via push button switching.
Newer PTT systems use voice over Internet Protocol (VoIP) for 3G digital PTT. For example, an air traffic controller communicates with aircraft via one radio frequency, and transmitted voice messages are shared between the controller and each airplane.
The PTT concept has been adopted by cellular systems to offer a service known as Push To Talk over Cellular (PoC), which allows end users to turn their cellphone into a walkie talkie with a much wider range.