Since HTML5 is still only a markup language, what is meant when people say HTML5 application? Please explain.
What is meant by an HTML5 application?
terminology;html5
An HTML5 application is an application that uses HTML5/Javascript/CSS3 as its primary means of achieving a User Interface.The term is significant, largely because this is considered a platform-independent way to get an application onto as many different mobile devices as possible.  Android and iOS are pretty much completely different, but both platforms will work with applications written in HTML5/Javascript/CSS3.  All you need is an HTML5 compliant browser.