My dad's identical twin was diagnosed with Parkinson's Disease. Will my dad have it?

Their father had it as well. Also the major question I have is, what is parkinson's disease (besides the shaking)????? Is it terminal?

not really. i found this study for you! PD=parkinson disease.
don't worry at all.

"If PD is inherited, such a tendency might be revealed in studies of twins. In a study of 43 pairs of identical twins and 19 pairs of non-identical twins, in which one of the twins had PD, it was found that in only one identical twin pair did both twins have PD. Thus, the frequency of PD in identical twins was similar to what would be expected by chance alone". from Abraham Lieberman, M.D.

If your uncle and your grandfather both had Parkinson's, it is very likely that it is the hereditary version. It is possible, however, that there is another cause.

Most people with Parkinson's disease are described as having idiopathic Parkinson's disease (having no specific cause). There are far less common causes of Parkinson's disease including genetic, toxins, head trauma, and drug induced Parkinson's disease.

How about going to reputable websites (medical websites ) to learn more about this disease? Maybe there is some genetic cause to this disease. But I do not think your dad will definitely get it, though he may have more propensity to get it. Just hope for the best and pray.

:-) Cheer up! life is still beautiful.