Prawn is a common name for small aquatic crustaceans with an exoskeleton and ten legs (members of the order of decapods), 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.

From Raymond Bauer in Remarkable Shrimps:

From the English Oxford Dictionaries:

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.

According to the crustacean taxonomist Tin-Yam Chan, "The terms shrimp and prawn have no definite reference to any known taxonomic groups. Although the term shrimp is sometimes applied to smaller species, while prawn is more often used for larger forms, there is no clear distinction between both terms and their usage is often confused or even reverse in different countries or regions." Writing in 1980, L. B. Holthuis noted that the terms prawn and shrimp were used inconsistently "even within a single region", generalising that larger species fished commercially were generally called shrimp in the United States, and prawns in other English-speaking countries, although not without exceptions.

Much confusion surrounds the scope of the term shrimp. Part of the confusion originates with the word's association with smallness; many shrimp species are small, about 2 cm (0.79 in) long, but some shrimp exceed 25 cm (9.8 in), such as Penaeus monodon. The expression "jumbo shrimp" can be viewed as an oxymoron, a problem that does not exist with the commercial designation "jumbo prawns". Larger shrimp are more likely to be targeted commercially and are often referred to as prawns, particularly in the Commonwealth of Nations.

The term shrimp originated around the 14th century with the Middle English shrimpe, akin to the Middle Low German schrempen, and meaning 'to contract or wrinkle'; and the Old Norse skorpna, meaning 'to shrivel up', or skreppa, meaning 'a thin person'. It is not clear where the term prawn originated, but early forms of the word surfaced in England in the early 15th century as prayne, praine and prane. According to the linguist Anatoly Liberman it is unclear how shrimp, in English, came to be associated with small, since no other language with Germanic origins associates shrimp with how large they are. "The same holds for Romance... it remains unclear in what circumstances the name was applied to the crustacean."