Sign vs disease . Tremors are a symptom/sign that can have many potential causes. Parkinson's is a disease due to a defined pathology (degenerative loss of Dopamine producing cells in the brain) that usually has a particular type of tremor as a symptom/sign. Essential tremor (aka familial benign tremor) is an even more common disorder than parkinson's, and it's tremor usually looks much different from pd tremor.
Symptoms. Resting tremor is a symptom of parkinsonism but tremors occur for other reasons. Tremor is a symptom and parkinsonism is a diagnosis.
Tremors not disease. Tremors occur secondarily to a variety of causes, including medications, thyroid problems, and a host of neurological mechanisms. Parkinsonian tremors occur when arms sitting at rest, essential hereditary tremors when arms outstretched. The problems occur at different ages and have varying courses and prognosis.