From KDE TechBase

    The plasmoid metadata.desktop file can provide the key


    It's a list, so one plasmoid can provide more than one feature

    name feature
    org.kde.plasma.launchermenu The plasmoid offers a "start menu" capability, a menu-based way to launch applications
    org.kde.plasma.time It's a clock in any form It's a calendar, or provides one
    org.kde.plasma.multitasking The plasmoid assists multitasking, such as a taskbar or a dock
    org.kde.plasma.filemanager Provides a filesystem view and some filemanager features
    org.kde.plasma.trash system trashcan access and control
    org.kde.plasma.virtualdesktops virtual desktop management tools, such as a pager or a button to trigger the show desktops effect
    org.kde.plasma.activities Activities management tools
    org.kde.plasma.notifications show notifications
    org.kde.plasma.powermanagement power management ifo, such as battery and brighness controls
    org.kde.plasma.removabledevices Removable devices info and access such as mount and unmount
    org.kde.plasma.multimediacontrols multimedia controls, such as info on what is now playing