Optical filters are devices that select or reject specific wavelengths or colors of light passing through them. They are commonly used in various optical systems to manipulate light by either transmitting or blocking certain wavelengths. Optical filters can be made of various materials such as glass, plastic, or specialized coatings, and can be designed to have a specific spectral bandwidth or cutoff frequency. They are used in a wide range of applications including photography, spectroscopy, telecommunications, and fluorescence microscopy.