What is a shiv in HTML5?
So, an HTML5 shiv basically allows new HTML5 elements to be styled using older styles.
How to use the HTML shiv
<!--[if lt IE 9]> <script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"> </script> <![endif]-->
How to download the HTML shiv
Shiv versus shim
There is absolutely no difference between a shiv and a shim. The person who coined the term shiv actually meant for it to be called “shim”, but the term shiv was the term that became more popular – although you are likely to come across “shim” as well
What is the difference between a shiv and a polyfill?
A polyfill is different from a shiv because, assuming your code is correctly written, even if you remove the polyfill script your code should still work just fine. However, if you remove a shiv, then your code will not work correctly (at least in older versions of IE) because of the issues with styling elements that are not recognized by earlier versions of IE.