What are visible depressions running across the width of the natural nail plate called?

Visible depressions running across the width of the natural nail plate are known as Beau's lines. These lines are indicative of a temporary disruption in the growth of the nail and can be caused by various factors such as illness, injury, or severe stress to the body. When the nail matrix (the tissue under the base of the nail) is affected, it results in the formation of these lines as the nail grows out.

In contrast, the other choices refer to different nail conditions or features that do not describe these specific depressions. Lentigines refer to small pigmented lesions on the skin, ridges can indicate other growth issues but are not typically crosswise depressions, and plicatured nails denote a nail condition that is twisted or deformed, which is unrelated to the horizontal lines seen with Beau's lines. Understanding the characteristics of Beau's lines is important for detecting underlying health issues and providing the appropriate care or referral.