Deflector dish

The deflector dish is a feature usually seen on Federation starships, facing foreward. The dish projects a force field ahead of the ship that deflects small debris out of the ship's path while it is travelling at warp speed. This field protects the ship from warp-speed collisions with micro-meteoroids and other small objects, since even interstellar dust could be harmful to the ship at such high speeds.

The starships of other major Star Trek civilizations usually do not have highly-visible deflector dishes, but they presumably have a less mechanisms that perform this function.