According to Matt Williams of Universe Today, the Universe we know encompasses our reality, and everything we see. The term “Universe” derives from the Latin word “Universum,” which Latin writers used to describe the cosmos as they saw it. The words cosmos and universe are used interchangeably by most astronomers. The origin of the cosmos is widely unknown aside from the Big Bang, which is by far the most accepted theory as to the origin of all matter. There are other theories, like the Oscillating Universe theory which proposes that the Universe as we know it goes through an infinite cycle of Bangs and Crunches.
What we know is that, by winding back the cosmological clock, all space converges to a singularity of infinite density which expanded outward in the “Big Bang.” This happened at (our best estimate) 13.8 billion years ago. While that part, and the history of the Universe is easily viewable to us now, the very, very earliest moments (10^-43 to 10^-11 seconds) are still a mystery. The closest we can come to simulating these conditions are in large particle accelerators.
The universe is a big place, 93 billion light years from visible end to visible end. It continues to expand ever faster and with it, our understanding of its origin.