A deflector beam, sometimes referred to as a meteoroid beam, was an energy discharge produced by a starship's main navigational deflector, for use in clearing obstruction's from the vessel's path, such as meteoroids. Highly adaptable, the beam could be reconfigured for a variety of purposes.
In 2254, the USS Enterprise encountered a disturbance traveling toward them at the speed of light, which was not deflected by the meteoroid beam. It was eventually realized, however, that they had encountered a radio wave, keyed to cause interference and attract attention, as a form of distress signal. (TOS: "The Cage", "The Menagerie, Part I")
In 2268, the crew of the USS Enterprise attempted to use a deflector beam to divert a large asteroid which was in danger of colliding with a planet populated by a society of peaceful Native Americans. To achieve the power levels necessary to do so, however, required chief engineer Montgomery Scott bypassing the relays and switching to manual control, as the overload would have been rejected by the automatic systems. Upon reaching the deflection point, the crew activated the deflectors, but found that the beam was not powerful enough to divert the asteroid any significant amount. Fortunately, it was later discovered that a large obelisk on the planet's surface was, in fact, a large deflector mechanism placed there by the Preservers, the race which transplanted the Native Americans to the planet in the first place. Activating the deflector, the crew of the Enterprise was able to divert the asteroid just in time to save the inhabitants from annihilation. (TOS: "The Paradise Syndrome")
In 2368, the crew of the USS Enterprise NCC-1701-D utilized a deflector beam to ionize the dust particles in a planet's atmosphere, in the form of a series of precisely-timed phaser blasts. The plan, which involved discharging all EPS taps through the phasers after an 8.3 second burst from the deflector dish, succeeded in converting the dust particles into high-energy plasma, which the Enterprise crew then absorbed with ship's shields, redirecting them harmlessly into space. (TNG: "A Matter of Time")
In 2376, the crew of the USS Voyager utilized a deflector beam to cut a path through a neutronic wavefront in which they had become trapped. As the wavefront was particularly powerful, this required siphoning power from nearly every system on the ship, including the transporters, replicators, and holodecks. (VOY: "Fair Haven")
A year later, while piloting the Delta Flyer, Harry Kim used the deflector beam to disable the weapons systems of an Annari vessel. Setting the beam to a narrow pulse of 0.4 microns, Kim fired as soon as the Annari weapons were fully-charged, triggering an overload in their phaser banks. (VOY: "Nightingale")