1784, "descent of a Hindu deity," from Sanskrit avatarana "descent" (of a deity to the earth in incarnate form), from ava- "off, down" (from PIE *au- (2) "off, away") + base of tarati "(he) crosses over," from PIE root *tere- (2) "to cross over" (see through). In computer use, it seems to trace to the novel "Snowcrash" (1992) by Neal Stephenson.