According to Lev Grossman writing in Time magazine (21 Feb 2011) “singularity” (noun) is defined as:
The moment when technological change becomes so rapid and profound, it represents a rupture in the fabric of human history.
Grossman also provides a brief history of the word’s usage in futurism:
The singularity isn’t a wholly new idea, just newish. In 1965 the British mathematician I.J. Good described something he called an “intelligence explosion”: “Let an ultraintelligent machine be defined as a machine that can far surpass all the intellectual activities of any man however clever. Since the design of machines is one of these intelligent activities, an ultraintelligent machine could design even better machines; there would then unquestionably be an “intelligence explosion,” and the intelligence of man would be left far behind. Thus the first ultraintelligent machine is the last invention that man need ever make.”
The word “singularity” is borrowed from astrophysics: it refers to a point in space-time–for example, inside a black hole–at which the rules of ordinary physics do not apply. In the 1980s the science-fiction novelist Vernor Vinge attached it to Good’s intelligence-explosion senario. At a NASA symnposium in 1993, Vinge announced that “within 30 years, we will have the technological means to create superhuman intelligence. Shortly after, the human era will be ended.”