[szszrk]

I hope you don't think that user-to-machine means that I have to stick my finger in a network switch? :)

Machine-to-machine is usually meant as traffic where neither of the sides is the client device (desktop, mobile etc). Often not initiated by user, but that's debatable.

I would say an server making a sync of database to passive node is machine-to-machine, while a user connection from his browser to webserver is not.