It was once called The Farmer's Disease but is now commonly called Parkinson's Disease, abbreviated to PD, or even just Parkinson's. It is a progressive neurological condition affecting movements such as walking, talking, and writing. One of a group of conditions called motor system disorders, which are the result of the loss of dopamine-producing brain cells. It is named after Dr. James Parkinson (1755-1824), the London doctor who first identified Parkinson's as a specific condition. It has also been called the Shaking Palsy because an early and highly visible symptom is often tremor - a shaking of the arms and/or legs. (If there are no other symptoms the shaking may be "Essential Tremor" - a less serious affliction than PD.)
The main symptoms are
Parkinson's is chronic and progressive, meaning that it persists over a long period of time (in fact there is no known cure) and that it gets worse over time.
There are many resources on the Internet that give good descriptions of Parkinson's and its symptoms. Rather than replicate them here check out the Links and Resources page.