Final answer:
Tinea unguium, also known as onychomycosis, is the fungal infection that affects toenails and fingernails.
Step-by-step explanation:
The fungal infection of the toenails and fingernails is called Tinea unguium, which is also known as onychomycosis. This condition is characterized by a yellowing, brittleness, and possible breakdown of the nails. Tinea infections are classified as cutaneous mycoses, which affect the skin, hair, and nails due to the presence of dermatophytes that feed on keratin. Other types of Tinea infections include Tinea corporis (ringworm), Tinea pedis (athlete's foot), and Tinea cruris (jock itch), each named for the area of the body they affect.