Trembling of the hands and other limbs, the so called human Tremor, is one of the most prominent symptoms of neurological, psychiatric and other diseases. While a mild, sometimes even difficult to realize trembling of the hands is always present in healthy persons, a tremor can become so severe, that the person is basically not able to live an unsupported life.
There are many different forms of tremor, for example the Parkinsonian tremor, a prominent symptom of Parkinson’s disease. Not all visible trembling of the limbs can be seen as pathologic. As mentioned above, a slight tremor is always present in every human, so the definition “pathologic” in this case is rather referring to a situation where the tremor is distracting the person in daily life.
For more information about tremor, please visit the NINDS Tremorinformation site, or Wikipedia.