What is the meaning of polyfills in HTML5

Question

Actually, I have no idea what polyfills are supposed to signify.

Is it a JavaScript library or a novel HTML5 technique?

This word is new to me compared to HTML5.

And what distinguishes shims, fallbacks, and polyfills from one another?

Answer 1

A polyfill is a JavaScript-based browser fallback that allows functionality that you expect to operate in contemporary browsers to work in older browsers, such as supporting canvas (an HTML5 capability) in previous browsers.

It's a kind of HTML5 method since it's used in combination with HTML5, but it's not part of HTML5, because polyfills may exist without HTML5 (for example, to support CSS3 techniques you want).