Official web site:

WebAssembly (abbreviated Wasm) is a binary instruction format for a stack-based virtual machine. Wasm is designed as a portable compilation target for programming languages, enabling deployment on the web for client and server applications.

WASI - WebAssembly System Interface, WASI is a modular system interface for WebAssembly.

A bare metal physical implementation of WebAssembly. That's right, a WebAssembly CPU.