The navigational deflector (also known as the deflector dish, deflector array, or main deflector) is a component installed on many starships, and was mainly used to deflect space debris, asteroids, and any other objects that may lie in a starship's path and potentially be a hazard.
On Federation starships the deflector was usually located at the front of the secondary hull and typically glows with a blue energy. Because of the deflectors ability to produce large amounts of energy and particles to very tight specifications they have often been utilised with minor modifications to help solve a variety of tasks: the USS Enterprise-B's dish was once modified to simulate a photon torpedo, the USS Enterprise-D's deflector was once modified to channel an extremely large amount of energy in the hopes of using it as a weapon against the Borg, the USS Defiant's deflector was once modified to be used as a single shot phaser, and the USS Voyager's deflector has been used to open a rift into fluidic space. (TNG movie: Star Trek: Generations; TNG episode: "The Best of Both Worlds, Part II"; DS9 episode: "Starship Down"; VOY episode: "Scorpion, Part II")
In 2372, Lieutenant Sean Hawk suggested several modifications that could be made to the USS Enterprise-E's main deflector that would allow the ship to travel at a higher velocity within the high particle density of the Pantera Nebula. Realising Hawk's potential, Captain Jean-Luc Picard ordered him to look in to designing and implementing those modifications. (TNG eBook: A Sea of Troubles)