Indented vertical lines down the nail plate that may be caused by illness or injury are called:

The term that accurately describes indented vertical lines down the nail plate, which may result from illness or injury, is furrows. Furrows appear as grooves along the nail's surface and can manifest due to various factors, including trauma or underlying health issues. These lines are typically more noticeable in cases of severe stress to the nail matrix and can serve as indicators of past health problems or physical trauma.

Ridges are generally raised lines that run along the length of the nail and can be a natural sign of aging. Beau's lines refer specifically to deeper horizontal indentations that cross the nail plate and are often associated with severe illness or interruption in nail growth. Onycholysis is a condition characterized by the separation of the nail from the nail bed, often seen in fungal infections or other health concerns. Understanding these distinctions helps in identifying the specific conditions affecting nail health.