A digital signature in electronic transactions is a cryptographic technique used to verify the authenticity and integrity of digital messages or documents. It provides a means to confirm that the message was created and sent by a specific individual, known as the signer, and that it has not been altered during transmission. Digital signatures use public-key cryptography, where a sender signs the transaction with their private key, and the recipient verifies it using the sender's public key. This technology enhances trust and security in online transactions.