The "Known Universe" refers to the vast expanse of space that scientists have observed and studied. It includes all the galaxies, stars, planets, and other celestial objects that can be detected using telescopes and other instruments. The observable universe is estimated to be about 93 billion light-years in diameter, containing billions of galaxies, each with millions or billions of stars. The study of the known universe helps astronomers understand the fundamental laws of physics and the origins of cosmic structures. Key concepts include the Big Bang, dark matter, and dark energy, which play crucial roles in the universe's expansion and evolution.