Exchanging in kids what the Bacco brilliantly said in his answer, the term refers to that moment or single point (from singular, hence the term singularity) in history in which technology (focused on AI - artificial intelligence) would become so advanced to the point that machines would become self-processing and infinite predictability, so that they would no longer be only slaves based on instructions and would go on to make broader and unlimited decisions, in a way superior and incomprehensible to human capacity.

In cinema such a situation has been approached in a fictitious way in films such as Matrix (1999), The Terminator of the Future (1984), A. I - Artificial Intelligence (2001), among others.

Some renowned scientists already predicted such an event decades ago. To name a few, like the well-known mathematician Alan Turing:

In his 1951 article entitled Intelligent Machinery: A Heretical Theory, Alan Turing wrote about machines that eventually will surpass human intelligence:

"once the machine thinking method has started, no it will take a long time to overcome our weak powers. ... In some at the moment, we must wait for the machines to take control, from way that is mentioned in Samuel Butler's Erewhon".

Another famous American scientist Vernor Vinge, introduced the term technological singularity in the January 1983 issue of Omni magazine specifically related to the creation of intelligent machines:

" soon we will create intelligences greater than ours. When this happen, human history will reach a kind of uniqueness, an intellectual transition as impenetrable as knotted space-time in the center of a black hole, and the world will pass far beyond ours understanding. This uniqueness, I believe, it already haunts several science fiction writers. This makes extrapolation impossible realistic for an interstellar future. To write a story of more than a century, it takes a nuclear war between ... so that the world remain intelligible".

Later developed the concept further in his essay the Coming Technological Singularity (1993):

" in thirty years, we will have the technological means to create superhuman intelligence. Soon after, the human age will be ended. [...] I think it's fair to call this event a singularity. It is a point at which our models should be discarded and a new reality it's valid. As we get closer and closer to this point, it will be wider and wider on human affairs until the notion make it a common place. However, when it finally happens, still it can be a big surprise and a bigger one unknown".

It is important to emphasize that for Vinge, uniqueness can occur in four ways:

1. the development of computers that are "awake" and superhuman intelligence.
2. large computer networks (and their associated users) can "waking up" as a superhuman intelligent entity.
3. computer / human interfaces can become so intimate that users can reasonably be considered superhuman smart.
4. biological science can find ways to improve the intellect natural human.

As the subject is wide and interesting, so as not to be too extensive, I finish the answer here. I hope it helped a little more in understanding.

I used as search source the site below, which still provides 17 definitions of the term relating their respective scientists:

Https://www.singularityweblog.com/17-definitions-of-the-technological-singularity/