The Jargon File (version 4.4.7, 29 Dec 2003):

demoparty
 n.

    [demoscene] Aboveground descendant of the copyparty, with emphasis
    shifted away from software piracy and towards compos. Smaller
    demoparties, for 100 persons or less, are held quite often, sometimes even
    once a month, and usually last for one to two days. On the other end of the
    scale, huge demo parties are held once a year (and four of these have grown
    very large and occur annually ? Assembly in Finland, The Party in Denmark,
    The Gathering in Norway, and NAID somewhere in north America). These
    parties usually last for three to five days, have room for 3000-5000
    people, and have a party network with connection to the internet.