From the Wikipedia article on Technological Singularity:

Technological singularity is a term with multiple related, but conceptually distinct, definitions. One definition has the Singularity as a time at which technological progress accelerates beyond the ability of current-day human beings to understand it. Another defines the Singularity as the culmination of some telescoping process of accelerating computation taking place in this universe since the beginning of human civilization or even life on Earth. Yet another defines the Singularity as the emergence of smarter-than-human intelligence, and subsequent cascading consequences that are not possible to predict or, perhaps, guide or even influence.