Multi-sig, short for multi-signature, is a security feature used in cryptocurrency transactions. It requires multiple private keys to authorize a transaction, rather than just one. This means that several people or devices must agree before funds can be moved, enhancing security and reducing the risk of theft. In a typical multi-sig setup, a wallet might require signatures from, say, three out of five designated users. This is particularly useful for organizations or groups, as it ensures that no single individual has complete control over the funds. Multi-sig wallets are often used in conjunction with Bitcoin and other blockchain technologies.