Singularitarianism refers to attitudes or beliefs favoring a technological singularity. The term was coined by Mark Plus, then given a more specific meaning by Eliezer Yudkowsky in his Singularitarian principles. "Singularitarianism", early on, referred to an principled activist stance aimed at creating a singularity for the benefit of humanity as a whole, and in particular to the movement surrounding the Singularity Institute. In Yudkowsky's later words:
Mark Plus coined the term "Singularitarian", but didn't do much with it; when I decided to build a Singularitarian movement, I asked Mark Plus for ownership of the word and was granted it; and I define the term to involve activism.
The term has since sometimes been used differently, without it implying the specific principles listed by Yudkowsky. For example, Ray Kurzweil's book "The Singularity Is Near" contains a chapter titled "Ich bin ein Singularitarian", in which Kurzweil describes his own vision. Other examples are this blog post and the song "I am the very model of a Singularitarian", whose protagonist's ambition to "expand his mental faculties by merging with technology" also suggests a more Kurzweilian view. Others have used "Singularitarian" to refer to anyone who predicts a technological singularity will happen.
Yudkowsky has (perhaps facetiously) suggested that those adhering to the original activist stance relabel themselves "elder Singularitarians".