Of course these were the days when computers were not connected to the network with permanent connections, so the whole shebang was based on dial-up services: if you copy a file it is copied to a spool and then sent onwards during the next time the system connects. This was extended by allowing to send files over multiple remote systems. So you might copy a file from computer A to computer C, and the file would travel first to computer B, then to C when B connected with that one.