These pages contain information on how KDE can make use of the MetaInfo data provided by the Freedesktop.org AppStream project.
MetaInfo files are used to describe a software component in a distribution. The metadata these XML files provide contains information about the public interfaces this component provides, the descriptions of the component, as well as additional things such as icon information and categorization. There are several special components, for example for applications, web-applications, fonts, codecs and input-methods. The information defined in these files is used by AppStream-compatible software centers (such as Apper or GNOME-Software) to display them to the user. In the following, we describe for different kinds of KDE software components how to write proper AppStream MetaInfo files. A project may ship multiple metadata definitions, for example if it ships an application and a library, or multiple applications.
Applications are (usually graphical) programs which show up in the applications menu, meaning they have a .desktop-file. You can read more about how to write metadata for them on the page about desktop-apps.
A generic component is a software project which doesn't fit into a specific category. This is usually a shared library or framework which wants to publish information about the public interfaces it provides in a distribution, to make it easier for developers to find the component in the distribution's repositories. You can find information on how to write metadata for a generifc component on the page about generic components.