Most of the interactive content you see on the web (besides Flash) is powered by JavaScript, initially created by Netscape Navigator developers in 1995. As with the rest of the internet, it has grown and changed a good deal since then, but it's not perfect. JavaScript is a high-level language, meaning basic functions like garbage collection are handled by the JavaScript VM. WebAssembly has been in the planning stages for years, as an alternative to JavaScript for low-level applications, and it is now enabled by default in Chrome Canary 58.

I'll spare you the detailed explanation of WebAssembly, but essentially if web applications (and games) need more control and/or processing power, they can choose to develop for WebAssembly instead of JavaScript. For example, multi-threaded tasks like video editing would be significantly easier to accomplish in WebAssembly due to how it handles threads and SIMD. And unlike Google's ill-fated Dart VM and the old Java plug-in, this already has cross-browser support. There are many more advantages, but that's the main summary.

If you have the latest version of Chrome Canary, you can try out this demo of a game ported to WebAssembly (the controls don't work on mobile, but it looks neat). It will likely take a while for the benefits of WebAssembly to be widely used, but perhaps we might see online versions of power tools like Photoshop and Premiere in the next few years.