What does 'Melanonychia' refer to?

Melanonychia refers to a medical condition where there is a significant darkening of the fingernails or toenails. This condition may be caused by increased melanin production or the presence of melanocytes in the nail bed. While options A, B, and D all describe changes in the appearance of nails, they do not specifically refer to darkening and are therefore incorrect. Additionally, inflammation of the nail bed is referred to as onychitis, and curving of the nails is known as koilonychia.