Voice Over Internet Protocol is a name of a family of technologies that allows transmission of voice over an established network connection. What is usually discussed, though, is Internet Telephony - bidirectional voice (and lately video) transmission over public networks.

VoIP questions should cover configuration of softphones, voice software (such as Asterisk) that runs on computers (no hardphones or PBXs) or troubleshooting VoIP quality and connectivity issues by means of computer hardware or software (tcpdump, wireshark).