STARFLEET DATABASE FILE: Deflector shields

Deflector shields are focused spatial distortions resulting in a deflective graviton field. This field effect is generated by wave-guides on the outer hull of the ship. Deflector shields have a significant fratricidal effect on the warp fields. Neither system can be operated at optimal efficiency when both are in operation. 
Like most force-field devices, the deflector system creates a localized zone of highly focused special distortion within which an energetic graviton field is maintained. The deflector field itself is emitted and shaped by a series of conformal transmission grids on the spacecraft exterior, resulting in a field that closely follows the form of the vehicle itself. This field is highly resistive to impact due to mechanical incursions ranging from relativistic subatomic particles to more massive objects at lesser relative velocities. When such an intrusion occurs, field energy is concentrated at the point of impact, creating an intense, localized spacial distortion.

Basically all this says is that the shields are a set of reversed gravity screens. if anything 'hits' the screens, the shield system reverses the gravitational acceleration in that zone, counteracting the force of the Photon Torpedo or whatever hits the shield. To the Torpedo, it will seem like it hit something solid... 
