Explanation: "Pan Pan" is the internationally recognized radiotelephone urgency signal. It indicates that a station has a very urgent message to transmit concerning the safety of a ship, aircraft, or person, or a person onboard, but it does not signify immediate danger to life or the vessel itself. This signal, spoken three times, takes precedence over all other communications except distress traffic. "Mayday" is the distress signal, indicating immediate grave danger to a vessel or person's life. "Securite" is the safety signal, used for important navigational warnings or meteorological information. "Seelonce Feenee" (or "Silence Fini") is used to announce the end of a radio silence period after a distress event, not as an urgency signal. These signals are part of the International Telecommunication Union (ITU) Radio Regulations, establishing a clear hierarchy for prioritizing maritime and aeronautical radio communications.