In short - you need Qlik Sense in order to implement responsive design.
I guess the best way to get the general description of the term is to Google it. When it comes to QlikView, the "out of the box" interface in QlikView is not responsive - it is not automatically re-sizing itself to fit into a smaller screen.
If you can't use Sense, then you should design your application based on the lowest resolution that your mobile devices can use. Perhaps you could have 2-3 versions of each sheet - full size, tablet size, and mobile size, and swap the versions based on the specific client.
