Whoever wrote the lyrics “You say tomato, I say tomahto” could just as well have added the verse, “You say shrimp, I say prawn.” The two words are used interchangeably in markets and restaurants everywhere. The textbooks may agree that a shrimp is a shrimp, but many people (and quite a few cookbooks) refer to this most popular of shellfish as a prawn.

Some people say the difference is size. In many parts of the country, small and medium shrimp are sold simply as shrimp, while large, extra-large, and jumbo shrimp are called prawns. Unfortunately, this “rule” doesn’t always hold. In some areas, all shrimp, small and large, are sold as shrimp, while in other regions, all you’ll find are prawns.

Purists may argue that the term “prawn” is reserved for the shrimp’s close relative, the Dublin Bay prawn. The Dublin Bay prawn resembles a shrimp, but it’s distinguished by its small pincer claws (similar to those on a lobster) and a narrower body. Sometimes called Florida or Caribbean lobsterettes or French langoustines, these shellfish can be hard to find in markets. And unlike shrimp, Dublin Bay prawns are usually cooked with their heads on. The claws make quite an attractive presentation, although they’re too tiny to render any meat.

In Italy, Dublin Bay prawns are called scampi, which has confused Americans even more. In the United States, scampi refers to a dish of large shrimp that are cooked with garlic and butter or olive oil.