It is a Spanish word with different meanings in different areas. In America, it is commonly used in the restaurant trade to refer to the meat of a squat lobster, which is neither a true lobster nor a prawn. it's more closely related to porcelein crabs and hermit crabs. in Spanish it means some species of prawns (crustaceans)
Langosta is a spiny lobster, found in the cays. It looks like a lobster, but without the claws.