This is actually a interesting question related to other questions having to with measuring distances on the cosmological scale in our universe.
If a galaxy is 10 billion light years away, this is generally taken to mean that a photon of light travels across space to the Earth for 10 billion years to get here. The path that photons take defines what we mean by distance, but because the geometry of the cosmos is curved by its content of matter and energy ( according to Einstein's theory of general relativity) these paths need not be straight. They are called geodesic curves. The time of flight along such curves is just the equivalent distance in light years. So in the above example, it took light 10 billion years to get to Earth.