dbus-1-doc 1.12.16-2ubuntu1 (s390x binary) in ubuntu focal

 D-Bus is a message bus, used for sending messages between applications.
 Conceptually, it fits somewhere in between raw sockets and CORBA in
 terms of complexity.
 .
 This package contains the API documentation for D-Bus, as well as
 the protocol specification.
 .
 See the dbus description for more information about D-Bus in general.