Here's a breakdown:
* Frankfurter: The name refers to the sausage itself.
* Frankfurt am Main: This is the city in Germany where the sausage is believed to have originated.
The name "frankfurter" has been used in English since the 19th century to refer to this type of sausage. Today, it's a common name for a type of hot dog, though the actual sausage made in Frankfurt is different.