A digital signature is a cryptographic technique that allows a person or entity to verify the authenticity and integrity of a digital message or document. It uses a pair of keys: a private key, which is kept secret, and a public key, which is shared with others. When a document is signed with a digital signature, it ensures that the document has not been altered and confirms the identity of the signer. Digital signatures are widely used in various applications, including email communications, software distribution, and financial transactions. They provide a secure way to sign contracts and agreements electronically, making the process faster and more efficient while maintaining trust and security.