The Free On-line Dictionary of Computing (30 December 2018):

Reverse Address Resolution Protocol
RARP
Reverse ARP

    (RARP) A protocol defined in RFC
   903 which provides the reverse function of ARP.  RARP maps
   a hardware address (MAC address) to an IP address.
   It is used primarily by diskless nodes, when they first
   initialise, to find their IP address.

   See also BOOTP.

   (1994-12-08)