2D Glasses convert 3D movies back into 2D, which sounds like a joke, but with over 10,000 currently in use in the United States alone, they're not. If you get headaches during 3D movies but are tired of complaining to your friends and family when they want to go see the 3D version, 2D Glasses are for you.
Note: 2D glasses work in 3D cinemas. However, they do not work at IMAX theatres.