The term used to describe abnormal hair loss is:

The term used to describe abnormal hair loss is "alopecia." Alopecia is a broader medical term that encompasses various types of hair loss, including complete baldness or patchy hair loss, and can occur due to various factors such as genetics, hormonal changes, autoimmune disorders, or stress.

It is important to understand that while other terms, such as hair thinning, telogen effluvium, and androgenetic alopecia, relate to specific types or patterns of hair loss, they fall under the umbrella of alopecia. Hair thinning generally refers to a gradual reduction in hair density and may not indicate complete hair loss, making it a less comprehensive term. Telogen effluvium describes a temporary condition where hair shedding occurs due to changes in the hair growth cycle, which results in noticeable hair loss but is often reversible. Androgenetic alopecia specifically refers to a hereditary condition that leads to gradual hair loss, commonly known as male or female pattern baldness. Therefore, "alopecia" is the most accurate and encompassing term for abnormal hair loss.