WebGL is a context of the HTML5 canvas element that enables hardware-accelerated 3D graphics in the web browser without a plug-in. In other words, it enables your browser to show some really beautiful visuals. Mrdoob/three.js - GitHub.
That means they can be passed around like any other value. One common use of this feature is to pass an anonymous function as a callback to another, possibly an asynchronous function. Processing.js. Demos below!