When astronomers say the Sun is an average-sized star, they mean it's average in terms of mass and luminosity compared to other stars in our galaxy.

Here's why:

* Mass: Our Sun is a yellow dwarf star, with a mass that falls within the typical range for this type of star. There are much larger and more massive stars out there, like red giants and supergiants, but there are also many smaller stars, like red dwarfs. The Sun's mass is roughly in the middle of the distribution.

* Luminosity: The Sun's luminosity (how much light it emits) is also in the middle of the range for stars. There are stars that emit much more light than the Sun, and others that emit much less.

It's important to note that even though the Sun is "average" in size and luminosity, it's still a tremendously powerful and important star for our solar system. It provides the light and heat necessary for life on Earth.

Let me know if you'd like to know more about different types of stars!