The Line Printer Remote protocol (or LPR) is a network protocol for submitting print jobs to a remote printer.
The Line Printer Daemon protocol/Line Printer Remote protocol (or LPD, LPR) is a network protocol for submitting print jobs to a remote printer.
The original implementation of LPD was in the Berkeley printing system in the BSD UNIX operating system; the LPRng project also supports that protocol.
The Common Unix Printing System (or CUPS), which is more common on modern Linux distributions, supports LPD as well as the Internet Printing Protocol (IPP).
The LPD Protocol Specification is documented in RFC 1179.
More information is available on Wikipedia.
