Così fan tutte (Thus Do They All) K. 588, is an opera by Wolfgang Amadeus Mozart. The libretto (the words) was written by Lorenzo da Ponte.
Così fan tutte is an opera buffa by Wolfgang Amadeus...
It means "This is how everyone does it." The full Italian title is "Così fan tutte, ossia La scuola degli amanti," and the old-fashioned, traditional translation normally used in English is, "Thus...