dbus-user-session 1.12.0-1ubuntu1 (amd64 binary) in ubuntu bionic

 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.
 .
 On systemd systems, this package opts in to the session model in which
 a user's session starts the first time they log in, and does not end
 until all their login sessions have ended. This model merges all
 parallel non-graphical login sessions (text mode, ssh, cron, etc.), and up
 to one graphical session, into a single "user-session" or "super-session"
 within which all background D-Bus services are shared.
 .
 Multiple graphical sessions per user are not currently supported in this
 mode; as a result, it is particularly suitable for gdm, which responds to
 requests to open a parallel graphical session by switching to the existing
 graphical session and unlocking it.
 .
 To retain dbus' traditional session semantics, in which login sessions
 are artificially isolated from each other, remove this package and install
 dbus-x11 instead.
 .
 See the dbus package description for more information about D-Bus in general.