What is the term used to describe the vast system of billions of stars, gas, and dust?

The term used to describe the vast system of billions of stars, gas, and dust is "galaxy." A galaxy is a massive, gravitationally-bound system that includes a wide range of stellar objects, interstellar gas, and dark matter. There are billions of galaxies in the universe, each containing millions to trillions of stars.

In contrast, a solar system refers specifically to a star and all the celestial bodies that are bound by its gravity, such as planets, moons, asteroids, and comets. A constellation is a pattern of stars in the night sky as observed from Earth, and these stars may not have any physical connection or be within the same galaxy. A nebula is a region of space filled with gas and dust, and while it may contain new stars forming within it, it does not encompass the concept of a galaxy as a whole system. Therefore, "galaxy" effectively captures the complexity and scale of this vast cosmic structure.