A set of rules specifying how to identify your station when linked over the internet to another station
A technique employed to “spot” DX stations via the internet
A technique for measuring the modulation quality of a transmitter using remote sites monitored via the internet
A method of delivering voice communications over the internet using digital techniques✓الإجابة الصحيحة
الشرح
VoIP means digitizing speech, breaking it into data packets and delivering it over the internet, which is the technology that lets radio systems in different places be linked. The other choices describe identification rules, DX spotting and transmitter measurement, none of which is what the term means.