It is a visualization of the area (the blue sphere) in the Milky Way galaxy containing all the stars visible in the night sky from Earth.
click to enlarge
All the stars that we can see with the naked eye are actually confined to a very small section of our galaxy. There are countless stars throughout the rest of the galaxy that are not visible from our relatively tiny planet. Of course, the Milky Way is just one galaxy among billions- each with billions of stars.
The scale of the universe is truly incomprehensible, and leaves the mind reeling at the size & complexity of our reality.