People often use the term "solar system" to refer to the planetary system that includes our own Sun and the celestial bodies orbiting around it, such as planets, moons, asteroids, and comets. This term is specific to our immediate cosmic neighborhood.
On the other hand, the term "universe" refers to the entirety of space and all the matter and energy within it, including all galaxies, stars, planets, and other celestial objects. The universe is vast and encompasses everything we know and observe.
The reason people commonly use the term "solar system" instead of "universe" is primarily due to the difference in scale and familiarity. The solar system is a relatively small and tangible concept compared to the vastness of the entire universe. It is something we can relate to on a more personal level as it includes our own home planet, Earth. People often study and discuss the solar system because it directly affects our lives and has a significant impact on our understanding of our place in the cosmos.
Conversely, the universe is so immense and complex that it can be challenging for individuals to comprehend or relate to it directly. The study of the universe as a whole falls within the domain of cosmology, a branch of astrophysics. While scientists and cosmologists explore and discuss the universe on a grand scale, it is not as commonly referenced in everyday conversations as the solar system.
In summary, people use the term "solar system" because it represents the celestial bodies revolving around our Sun and is closer to our immediate surroundings, whereas the term "universe" refers to the entirety of space and is more vast and abstract in nature.