Found this pretty good explanation:
Parametric vs. Graphic Equalizers
A graphic equalizer has usually fixed frequency and Q value. The layout of a graphic equalizer is the typical sliding controls arranged by frequency. The advantage of a graphic equalizer is that in the way it is laid out, it is easy to see what frequency is being boosted or cut and any person without much experience can adjust it. Since a graphic EQ has fixed frequencies and Q, it has limitations on what it can control.
A parametric equalizer consists of knobs that are turned to desired levels, have adjustable frequencies and (usually) Q. The advantage of parametric equalizers is a much greater control, since frequencies and Q values can be adjusted. On the other hand, a parametric equalizer is much harder to adjust than a graphic EQ, requiring an experienced person and measuring equipment.
It's all beyond me. Parametric EQ would seem to be the real deal EQ but because of it's complexity, not very user friendly. Wish they'd just provide some pre-programmed examples you could scroll through to hear the difference.