What does Boxing Day have to do with boxing?
(uucp) A Unix utility program and protocol that allows one Unix system to send files to another via a serial line which may be a cable going directly from one machine's serial port to another's or may involve a modem at each end of a telephone line.
Software is also available to allow uucp to work over Ethernet though there are better alternatives in this case, e.g. FTP or rcp for file transfer, SMTP for electronic mail or NNTP for news.
The term is now also used to describe the large international network which uses UUCP to pass Usenet news and electronic mail, also known as "UUCPNET".
Unix manual page: uucp(1).
See also cu, uuencode.