A year is the length of time it takes for a planet or asteroid to complete a full orbit of its star. As you probably already know, the Earth orbits the Sun which is its star. An Earth Solar Year is 365 days or 366 roughly every four years. Admittedly, the calculation for a leap year is a little more complex involving centuries but lets keep it nice and simple for now.
Mars has its own year, it is referred to as a Martian Year and that is 687 days. The further you move from the Sun, the longer that object's year get. Pluto, although not a planet having been downgraded in 2006 by the I.A.U. has the longest year of the main solar system objects. Pluto's year is 248 Earth Years.
Further out is Eris, a Kuiper Belt Object who discovery led to the demotion of Pluto. A Erisian year is 558 years because it orbits so far out
Before we go further out, here's an interesting fact, the planet Venus takes 224.65 days to orbit the Sun and is about the same size as the Earth. The time it takes to complete a day is longer than it takes to orbit the Sun. It also rotates in the opposite direction to the Earth, most likely caused by a collision during the birth of .
What is the Galactic Year?
Our Sun orbits the Supermassive Black Hole that is at the centre of our galaxy, the Milky Way galaxy at a distance of about 27,000 Light Years. You'll probably be surprised to hear that the Canis Major Dwarf Galaxy is nearer to us than the galactic centre.
Stars in an Elliptical Galaxy such as the Milky Way orbit the centre and the Milky Way is no different. The time it takes for the Sun to complete a full orbit of the Supermasssive is known as the Galactic Year. There might be an Universe Year but we'll never know probably. 
How Long is a Galactic Year?
The time it takes to complete a full orbit of the galaxy is about 225 - 250 million Earth years. 250 Million Years ago was the Triassic Period when the first dinosaurs were walking the Earth. If we turned the time back one Galactic Year, Earth would be much different, no Internet, no Mobiles, not even humans could be found orbiting the Earth.
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