WebRTC is a technology standard for doing Real Time Communications via a browser. To put it another way, WebRTC allows you to use a browser to make a phone call. Twilio Client has been modified to use WebRTC as an alternative to our original Twilio Client, which uses Flash to connect calls.
WebRTC is designed to work as a native part of a browser and provides a better experience for users. WebRTC also uses more advanced audio codecs than the Flash version of Twilio Client, this means improved audio quality.