Question

When we say that a galaxy is 5000 light years from earth we are actually describing

Answer 1

Hagrid's right, it defines withing the speed of light within a year. 

Answer 2

A light year refers to a very big amount of distance and is a measurement termed as an astronomical unit of measure. When you say that a galaxy is 5,000 light years away we are actually describing the speed of light within a year. One light year is actually equivalent to 9, 500, 000, 000, 000 kilometers. Just imagine how big or how far that galaxy is when you multiply those kilometers by 5,000?