HTML5 Canvas Element Tutorial
When using canvas, it's important to understand the difference between the canvas element and the canvas context, as often times people get these confused. The canvas element is the actual DOM node that's embedded in the HTML page. The canvas context is an object with properties and methods that you can use to render graphics inside the canvas element. The context can be 2d or webgl (3d).
Each canvas element can only have one context. If we use the getContext() method multiple times, it will return a reference to the same context object.