The disk of the Milky Way contains most of the gas and dust in the galaxy. It is the area where most of the new stars are formed. The material found in the disk takes the form of spiral arms. When viewing the sky it is the disk that provides the faint band of light seen across the sky; which comes from the stars of our galaxy the Milky Way.
The disk is very thin only 1000 light years thick in comparison to width of the galaxy which is around 100,000 light years across. The Sun is approximately 10,000 light years from the centre of the galaxy.