Creative Commons is a type of copyright that gives creators a way to share their work for free while retaining ownership. They offer six different licenses, and all a creator needs to do is attach one to his or her work. CC licensed materials are great for music, photos, sound effects, and more. You must be sure to follow the rules of the CC licenses, but they also give a lot more freedom than traditional copyright and are much easier to understand.
Please give credit when using Creative Commons material. The creators are letting you use their material for free, so it's the least you could do.
Want to learn more about Creative Commons, how it works, or how to cite it? Check out this useful infographic.