ARPA

agency of the US Department of Defense that established the ARPANET in 1968

The acronym ARPA has several meanings:The .arpa domain name expands to "Address and Routing Parameter Area"Advanced Research Projects Agency was renamed to Defense Advanced Research Projects Agency (DARPA) in 1972Automatic Radar Plotting AidAverage Revenue Per AdvertiserArchaeological Resources Protection Act
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.arpa is an Internet top-level domain (TLD) used exclusively for Internet-infrastructure purposes. It does not function as a normal TLD where websites are registered, but rather as a meta-TLD used to look up addresses, and for other purposes.The .arpa TLD was originally intended to be a temporary measure to facilitate the transition to the Domain Name System. The ARPANET was the predecessor to the Internet established by the United States Department of Defense Advanced Research Projects Agency (ARPA), and when the Domain Name System was introduced in 1985, ARPANET host names were initially converted to domain names by adding .arpa to the end. Hostnames in other networks were also sometimes converted to pseudo-domain-style addresses by adding endings such as .uucp and .bitnet, though these were never added to the Internet root as formal TLDs. Domain names of this form were rapidly phased out by replacing them with domain names using the other, more informative, TLDs.
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n. ARPA

Arpanet, Advanced Research Projects Agency net, wide area computer network established in 1968 that primarily connected universities and research centers, predecessor of the Internet (Computers)

Advanced Research Projects Agency net, large communications network which preceded the Internet

n. harp, large stringed instrument with an upright triangular frame which is played by plucking the strings with the fingers (Music)