(National Science Foundation NETwork) The network funded by the U.S. National Science Foundation, which linked five supercomputer sites across the country in the mid-1980s. Universities were also allowed to connect to it. In 1988, it was upgraded from its original 56 Kbps lines to T1 circuits. By the early 1990s, NSFnet was using a T3 backbone and served as the primary Internet backbone until 1995, when the Net became commercialized. See ARPAnet.