What is Galaxy

1. You are one of the billions of people on our Earth. Our Earth orbits the Sun in our Solar System. Our Sun is one star among the billions in the Milky Way Galaxy. Our Milky Way Galaxy is one among the billions of galaxies in our Universe.
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Meaning of universe

1. All space-time, matter, and energy, including the solar system, all stars and galaxies, and the contents of intergalactic space,regarded as a whole.

2. A hypothetical whole of space-time, matter, and energy that is purported to exist simultaneously with but to be different from thisuniverse: an alternate universe.

3.

a. A model or conception of the earth and everything else that exists: "Apart from celestial beings, the aboriginals' universe contained spirits of the land and sea" (Madhusree Mukerjee).

b. The human race or a subset of it: "It was a universe that took slavery for granted" (Adam Hochschild).

4. A sphere of interest, activity, or understanding: "their almost hermetically sealed-off universe of part-time jobs and study andimprovised meals" (Sue Miller).

What is universe ?

 all of space and everything in it including stars, planets, galaxies, etc.

 an area of space or a world that is similar to but separate from the one that we live in

 the people, places, experiences, etc., that are associated with a particular person, place, or thing