The phrase "black sheep" is an idiomatic expression that refers to a person who is considered to be different from or not conforming to the norms of their family, group or society. The term originated in the 18th century when black was used as a symbolic color to describe something or someone that was unconventional or unusual. In its original context, "black sheep" referred specifically to a sheep with a dark coat, which was considered rare and valuable at the time. Today, however, the phrase is commonly used in a more figurative sense to describe an individual who behaves in an unexpected or unorthodox manner, often in contrast to their family members or peers.