Prawn

Prawn is a common name for small aquatic crustaceans with an exoskeleton and ten legs , some of which are edible. The term prawn is used particularly in the United Kingdom, Ireland, and Commonwealth nations, for large swimming crustaceans or shrimp, especially those with commercial significance in the fishing industry. Shrimp in this category often belong to the suborder Dendrobranchiata. In North America, the term is used less frequently, typically for freshwater shrimp. The terms shrimp and prawn themselves lack scientific standing. Over the years, the way they are used has changed, and in contemporary usage, the terms are almost interchangeable. The terms shrimp and prawn are common names, not scientific names. They are vernacular or colloquial terms, which lack the formal definition of scientific terms. They are not taxa, but are terms of convenience with little circumscriptional significance. There is no reason to avoid using the terms shrimp or prawn when convenient, but it is important not to confuse them with the names or relationships of actual taxa.

Source: Wikipedia