WebAssembly is a new type of code that can be run in modern web browsers — it is a low-level assembly-like language with a compact binary format that runs with near-native performance and provides languages such as C/C++ with a compilation target so that they can run on the web. It is also designed to run alongside JavaScript, allowing both to work together.
In a nutshell
WebAssembly has huge implications for the web platform — it will provide a way to run code written in multiple languages on the web at near native speed, with client apps running on the web that previously couldn’t have done so.
Read more at Mozilla Developer Network
