They explain Kirigami:
Kirigami UI isn't just a set of components, it's also a philosophy: It defines precise UI/UX patterns to allow developers to quickly develop intuitive and consistent apps that provide a great user experience. Some concepts are: Actions are available in two drawers and additionally through some shortcuts (buttons or swipes); actions and options are distinguished into global ones and contextual ones, put in two different drawers in the opposite vertical sides of the screen; app's content is organized in pages that you can browse through with horizontal swipes. The Kirigami Components for smartphones are optimized to allow easy navigation and interaction with just one hand, making it ideal for using applications casually "on the move". Kirigami UI is not only for smartphone applications, however: It will allow to create convergent applications, which are not simply the exact same user interface scaled to different sizes, but morphing between optimized interfaces based on the input method and screen size, changing as the context changes (e.g. flipping over a convertible, docking a phone). Another important concept is non-invasive pop-ups to undo an action, rather than confirmation dialogs.
As Kirigami aims to seamlessly integrate with the basic sets of controls offered by QtQuick, such as QtQuickcontrols, it does not duplicate the effort to provide essential controls such as buttons and text input fields, but provides ready to use, high level controls to implement its design philosophy and UX guidelines.
More details at dot.kde.org.