Which term refers to an abnormal reduction of calcium?

The correct term for an abnormal reduction of calcium is hypocalcemia. This term specifically refers to low levels of calcium in the blood, which can lead to various symptoms and health issues, including muscle cramps, tingling sensations, and in severe cases, cardiac disturbances.

In contrast, calcipenis is not a widely recognized medical term; it does not specifically denote low calcium levels in any recognized medical literature. Calciosis refers to an abnormal accumulation of calcium in tissues, which is the opposite of having too little calcium. Osteopenia refers to lower than normal bone density and is related to calcium's role in bone health but does not directly indicate blood calcium levels. Thus, hypocalcemia accurately describes the condition of reduced calcium, directly aligning with the question's requirements.