The acronym ARPANET refers to the pioneering packet-switching network developed by the U.S. Department of Defense, considered the precursor to the modern Internet. Established in the late 1960s, ARPANET allowed multiple computers to communicate over a single network, paving the way for the development of networking protocols like TCP/IP. Its innovative architecture fostered collaboration among researchers and laid the groundwork for the interconnected global communication systems we use today.