Tremor has been defined in a consensus discussion as an involuntary, rhythmic, oscillating movement of any part of the body1. Its rhythmic aspect is very characteristic and distinguishes it from many other movement disorders such as dyskinesia, dystonia, or myoclonus.
A basic classification is tremor at rest and tremor with activity.
At rest does not mean during sleep because then the tremor usually has disappeared, but when the body part is fully supported against gravity. For example, if you sit with your arms on the chair back. This is called the resting tremor.
An action tremor is present when you adopt a certain position or move a body part. An action tremor is further divided into kinetic tremor, postural tremor, and intention tremor.
A kinetic tremor occurs when performing a movement, for example grabbing a cup.
A postural tremor occurs when the affected body part is held against gravity in a certain position (for example outstretched arms).
An intention tremor is characterized by a shocking movement when approaching the target. This can be tested with the finger-to-nose (with closed eyes, let the finger go to the nose in a wide arc, alternating left and right finger).