Define 'alopecia'.

Alopecia is defined as hair loss or baldness, which encompasses a variety of conditions that can lead to the reduction or complete absence of hair on the scalp or other parts of the body. This term is used broadly in the medical field to describe different forms of hair loss, including conditions such as alopecia areata (which results in patchy hair loss), androgenetic alopecia (commonly known as male or female pattern baldness), and other types.

In contrast to other options, abnormal hair growth refers to excessive hair growth that can occur in unusual areas, while a dry scalp condition addresses issues related to scalp health rather than hair loss. Thinning hair over time, although related to hair loss, doesn't encompass the full scope of what alopecia can denote, as it may refer specifically to a gradual decrease in hair density rather than baldness. Understanding these differences helps clarify why the definition of alopecia centers specifically on hair loss.