ARPA

1. Short for Advanced Research Projects Agency, ARPA is an agency formed in the United States as a reaction to the launch of the Soviet Union's launch of Sputnik in 1957 that was lead by Dr. J.C.R. Licklider to help fund and promote research. This agency help create ARPANET and was renamed to DARPA in 1972.
2. Short for Address and Routing Parameter Area, .arpa is a Top Level Domain that was originally created for transitions from ARPANET hostnames to the newer DNS type names in the late 1980's.

Also see: ARPANET, IPTO