Onychorrhexis is best described as?

Onychorrhexis refers specifically to a condition characterized by split or brittle nails. This condition manifests as ridges or grooves along the nail surface, which can lead to chipping and breakage. Factors that can contribute to onychorrhexis include excessive exposure to chemicals, frequent manicures, or health issues that affect the nail's structure.

Understanding the other options provides additional context for why they are not correct. The first option describes an abnormal curvature of the nail, known as onychoauxesis, which is different from the brittleness associated with onychorrhexis. The second option involves separation of the nail from its nail bed, a condition referred to as onycholysis, which is unrelated to brittleness. The last option discusses brown or black splinters under the nail plate, which could indicate a bleeding or trauma issue, but does not pertain to the structural integrity or brittleness of the nail itself. Thus, onychorrhexis is accurately defined as having split or brittle nails.