WebRTC stands for "Web Real-Time Communication," and it is a technology that enables real-time communication directly between web browsers and other applications. It allows for audio and video communication, as well as data sharing, without the need for additional plugins or software installations.
WebRTC can be used to determine your actual IP address, since in browsers, those requests bypass the proxy and VPN tunnels. This can deanonymize you. By turning on WebRTC Slayer, you will disable WebRTC in your browser, limiting the chance of an IP leak.
By enabling this feature to prevent leaks, some WebRTC-based applications will not work.