A Set structure, as used in many programming languages, is a collection of distinct elements where each item is unique, and no duplicates are allowed. This data structure is especially valuable when you need to efficiently check the existence of an item, maintain an organized collection of items without repetition, or quickly retrieve unique elements. Solidity programming language for Ethereum smart contract development does not natively support the Set data structure. Developers need to create their own structures or utilize external libraries to replicate Set functionalities, such as ensuring the uniqueness of elements within a collection.