Lens Hood

In photography a lens hood is a device used on the front site in lens.

Its block the sun or other  light source.

Lens hoods many also be used to protect the lens from scratches and elements without having to put on a lens cover. 

                          

                                        Lens filter

In photography a filter is a camera accessory consisting of an optical filter that can be inserted into the optical path. The filter can be of a square or oblong shape and mounted in a holder accessory, or, more commonly, a glass or plastic disk in a metal or plastic ring frame, which can be screwed into the front of or clipped onto the camera lens.

More information:https://en.wikipedia.org/wiki/Photographic_filter