Final answer:
Alopecia refers to the absence of hair, which can be caused by various factors such as genetics, autoimmune disorders, hormonal changes, and certain medical conditions.
Step-by-step explanation:
The term 'alopecia' refers to the absence of hair. It is a condition characterized by partial or complete hair loss, which can occur on the scalp or other parts of the body. Alopecia can be caused by various factors such as genetics, autoimmune disorders, hormonal changes, and certain medical conditions. For example, alopecia areata is an autoimmune disease that causes hair loss in patches, while androgenetic alopecia is a genetic condition that leads to gradual hair thinning.