WebAssembly is a low level language that works in binary and close with the machine code. It defines an AST in a binary format. In this language, you can create and debug code in plain text format. It made popular appearance in many browsers last year and is catching on due to its ability to run heavier apps with speed on a browser window. There are Tools and languages built for it.
Why are developers excited about WebAssembly?
Developers are excited about this as it can potentially run heavy desktop games and applications right inside your browser window. As Mozilla shares plans to bring more functionality to WebAssembly, modern day web browsing will become more robust.
However, the language used by this, WASM, poses some security threats. This is because WASM binary applications cannot be checked for tampers. Some features are even being held back from WebAssembly till it is more secure against attacks like Spectre and Meltdown.