Which condition is characterized by hair loss?

Alopecia is the medical term specifically used to describe hair loss, which can occur for a variety of reasons, including autoimmune disorders, genetics, and other health conditions. In alopecia, hair may thin or fall out in patches or may affect the entire scalp or body, depending on the type. This condition is well-defined and recognized in both clinical settings and common usage, making it the clear choice when identifying a condition characterized by hair loss.

Other conditions listed, such as anemia, anaphylaxis, and angina, do not inherently involve hair loss. Anemia refers to a deficiency in red blood cells or hemoglobin, typically leading to fatigue and weakness. Anaphylaxis is a severe allergic reaction that can be life-threatening and presents with symptoms such as difficulty breathing, swelling, and hives, but not hair loss. Angina is a related to chest pain due to reduced blood flow to the heart muscle, primarily affecting cardiovascular health rather than hair. This understanding solidifies alopecia as the correct answer in the context of the question posed.