How is 'universe' defined in physics astronomy and cosmology?

Answer 1

The universe is the totality of intelligible, perceptible, and quantifiable reality that is the focus of human scientific research. It is a four-dimensional space-time continuum consisting of matter, energy, and forces. The universe consists of both inanimate matter (e.g. planets, stars, galaxies, asteroids, comets) and animate matter (e.g. plants, animals, humans, bacteria, fungi). The four fundamental forces in the universe are gravitation, electromagnetism, and the strong and weak nuclear forces.

OR: The universe is everything, or the universe is everything around here -- thus, some talk about other universes. Sometimes the other universes are separated by distance, sometimes by time, sometimes by other imaginary conditions. The universe of real numbers does not include the square root of negative one -- another use of the word universe.