Grad filter (Graduated)
Graduated filters are usually neutral density types (more commonly called ‘ND Grad'), with the ND effect on one half gradually blending to the other clear half. Useful for balancing lighter skies with darker foreground detail.
ND filter (Neutral density)
Neutral Density filters reduce all wavelengths of light equally, so that the final result shows no colour bias. Useful for extending exposure times, such as when trying to capture motion blur.
UV filter (Ultraviolet)
Ultraviolet filters block UV light from entering the lens. As they have almost no effect on images in everyday use, many people keep these on their lenses permanently to protect the front element from any damage.
The most useful filter, a polariser sorts incoming light into a single polarity. By doing so, it can deepen blue skies and minimise reflections in water or glass, for example.