(covers information from several alternate timelines)
The deflector control room, also known simply as the deflector room or Deflector Control, was the area of a starship from which repairs and modifications could be made to the ship's deflector relays and similar systems, most notably the main navigational deflector.
In 2293, Captain James T. Kirk entered the deflector room of the USS Enterprise-B in order to modify the main deflector dish to emit a resonance burst that would allow the vessel to escape from a crippling energy ribbon. Kirk was able to complete the modifications, allowing the Enterprise-B to escape, before an energy tendril from the ribbon struck the ship, destroying the deflector room and apparently killing Kirk. (Star Trek Generations)
During the Borg's attempt to assimilate the USS Enterprise-E in 2373/2063, the Borg suddenly halted their advance when they took deck 11, the location of the vessel's deflector control room. The Borg hoped to use the deflector dish to construct an interplexing beacon to contact the Borg Collective of the 21st century, but were stopped by Captain Jean-Luc Picard, Lieutenant Commander Worf, and Lieutenant Hawk. (Star Trek: First Contact)
After a contingent of Borg beamed aboard the Voyager, they were trying to access Deflector Control and realign the deflector array emitters to contact the Borg Collective. As a final decision, Commander Chakotay ordered Harry Kim to depressurize the cargo bay and vent the Borg into space. (VOY: "Scorpion")
In 2374 of an alternate timeline, a heavily damaged USS Voyager lost its navigational deflector shields along with many other critical systems during the Year of Hell. Encountering a moving micrometeoroid field, the ship was vulnerable to hull erosion and began to suffer damage. Captain Kathryn Janeway restored the deflector manually, although she was badly burned with third-degree burns due to a massive fire in Deflector Control. (VOY: "Year of Hell, Part II")