Tinea unguium, also known as onychomycosis, is a fungal infection that affects the nails. It typically begins as a white or yellow spot under the nail and can spread to other nails. There are several synonyms used to describe this condition, including nail fungus, fungal nail infection, and toenail fungus. Other related terms include dermatophytic onychomycosis, distal subungual onychomycosis, and proximal subungual onychomycosis. Regardless of the specific term used, the condition is usually caused by exposure to fungus in warm and moist environments. Treatment typically involves antifungal medications and proper nail hygiene to prevent recurrence.