cdnjs is a free distributed JS library delivery service.
Internet Information Services (IIS) is an extensible web server software created by Microsoft for use with the Windows NT family.
jQuery CDN is a way to include jQuery in your website without actually downloading and keeping it your website's folder.
jQuery is a JavaScript library which is a free, open-source software designed to simplify HTML DOM tree traversal and manipulation, as well as event handling, CSS animation, and Ajax.
PHP is a general-purpose scripting language used for web development.
Stellar.js is a JavaScript library and jQuery plugin specifically designed to deliver parallax scrolling effects for web pages.
Unpkg is a content delivery network for everything on npm.