The galactic year is a unit of measurement of time.
Definition of the galactic year
In much the same way the Earth orbits around the Sun, the solar system orbits around the center of the Milky Way Galaxy. A galactic year is the time it takes for the Sun to come back at the same spot after orbiting around the galaxy once.
The distance to cover is such that, even at a speed of 220 km/s, it takes the Sun and the solar system approximately 225 million years to complete it.
Value
One galactic year is 225000000 years. [source]
Some Facts
The galactic year is so long it is hard to grasp how much. Even the Earth, with an estimated age of 4.55 billion years, is only just a little over 20 galactic years old.
On this kind of timescale the continental drift becomes obvious. The Earth of a galactic year ago would seem like an alien planet for us.
Dinosaurs were the dominant terrestrial life and would continue to be for 160 million years. While the mammals of that time were probably nocturnal shrew-like critters.
And it's not just life, the planet itself was unrecognizable with only one supercontinent encompassing all the landmass called Pangea.
You can't help but wonder what the Earth will look like in another 225 million years.