Heroku is a cloud platform as a service (PaaS) supporting several programming languages.
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.
Lightbox is small javascript library used to overlay images on top of the current page.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.