Sunnydale is the name of the system, the star, and the primary colonized world.  Well, technically they call the star Sunny, but that’s getting picky from an outside point of view.  The world is a lovely place to live, with similar gravity, atmospheric pressure, and temperature ranges to that of Earth.  She’s slightly larger, giving her much more land to live on.  In general, she’s one of the most comfortable worlds humanity has colonized in our march to the stars.