Here are the data structures with brief descriptions:

libinput	A handle for accessing libinput
libinput_device	A base handle for accessing libinput devices
libinput_device_group	A base handle for accessing libinput device groups
libinput_event	The base event type
libinput_event_device_notify	An event notifying the caller of a device being added or removed
libinput_event_keyboard	A keyboard event representing a key press/release
libinput_event_pointer	A pointer event representing relative or absolute pointer movement, a button press/release or scroll axis events
libinput_event_switch	A switch event representing a changed state in a switch
libinput_event_tablet_pad	Tablet pad event representing a button press, or ring/strip update on the tablet pad itself
libinput_event_tablet_tool	Tablet tool event representing an axis update, button press, or tool update
libinput_event_touch	Touch event representing a touch down, move or up, as well as a touch cancel and touch frame events
libinput_interface	Libinput does not open file descriptors to devices directly, instead open_restricted() and close_restricted() are called for each path that must be opened
libinput_seat	The base handle for accessing libinput seats
libinput_tablet_pad_mode_group	A mode on a tablet pad is a virtual grouping of functionality, usually based on some visual feedback like LEDs on the pad
libinput_tablet_tool	An object representing a tool being used by a device with the LIBINPUT_DEVICE_CAP_TABLET_TOOL capability