VoIP stands for Voice over IP.
VoIP is an umbrella term for all voice and video real time communications over the internet. In that sense, WebRTC is a subset of VoIP.
The WebRTC Glossary is an ongoing project where users can learn more about WebRTC related terms. It is maintained by Tsahi Levent-Levi of BlogGeek.me.
Looking to learn more about WebRTC?
Check my WebRTC training courses