Specifically, it's the browser engine that spun out of Mozilla's early efforts towards a rust-based browser, and is one of the motivating projects for the entire Rust ecosystem
Yes, Servo is an embeddable web browser / webview, like Chromium Embedded Framework. (CEF)
Electron = Node.js + CEF
Tauri = Rust + webview
Tauri has an experimental branch to use Servo to provide a bundled webview. Currently it relies on a system-level webview, like Edge on Windows, Safari on MacOS, and webkit-gtk on Linux.