A shiver, also known as a tremor, is an involuntary response of the body that often occurs when a person feels cold, scared, or excited. It involves rapid muscle contractions and relaxations, which can create a shaking sensation. Shivering helps generate heat to maintain body temperature in cold environments. Tremors can also refer to rhythmic shaking movements that may affect various parts of the body, such as the hands or legs. They can be caused by several factors, including Parkinson's disease, anxiety, or fatigue. Understanding the underlying cause is essential for effective management and treatment.