The term MOFFO SOLO is a combination of two words, 'Moffo' and 'SOLO'. Moffo is the surname of the Italian-American soprano Renata Tebaldi, who was one of the most acclaimed opera singers of the 20th century. SOLO is a musical term that refers to a single performer or instrument playing alone. Therefore, the crossword solution ARIA refers to a SOLO vocal piece, usually from an opera, which is sung by a single performer.