Which of the following nail disorders is associated with fungal infections?

Onychomycosis is the term specifically used to describe fungal infections of the nails. This condition can lead to various symptoms, including discoloration, thickening, and possible separation of the nail from the nail bed. Fungi thrive in warm, moist environments, which makes nails a suitable host for such infections. This disorder ultimately affects the health and appearance of the nails, often requiring antifungal treatment for correction.

Other choices mention different nail disorders that do not specifically relate to fungal infections. For example, onychocryptosis is associated with ingrown nails, onychauxis refers to a thickening of the nails without a fungal component, and pterygium involves abnormal tissue growth around the nail, typically as a result of injury or inflammatory conditions. Hence, onychomycosis stands out as the correct answer since it directly links to fungal involvement in nail disorders.