Which of the following best describes tremors?

Tremors are best described as involuntary movements or shaking, which makes option C the most accurate description. Tremors can occur in various contexts, including medical conditions such as Parkinson's disease, multiple sclerosis, and certain metabolic disorders. They typically manifest as rhythmic oscillations of a part of the body, often affecting the hands or limbs, but can also involve other areas.

Involuntary muscle contractions, as suggested in one option, encompass a broader range of muscle activities that may not result in the rhythmic, oscillatory motion characteristic of tremors. Excessive movement combined with anxiety may reflect a general state of hyperactivity or fidgeting but does not capture the specific nature of rhythmic shaking. Finally, extreme fatigue and weakness relate to exhaustion or lack of strength, which are distinct from the involuntary shaking that defines tremors. Hence, the description in option C accurately encompasses the essence of what tremors are in a clinical context.