A digital signature uses asymmetric cryptography to bind a signer to a document. The signer's private key creates a signature over the document's hash; anyone with the corresponding public key can verify the signature and confirm the document hasn't changed.
Digital signatures provide three guarantees: authenticity (the signer is who they claim to be), integrity (the document hasn't been altered), and non-repudiation (the signer can't later deny signing). They're a specific implementation of the broader 'electronic signature' concept.
Digital signatures are required for qualified electronic signatures (QES) under eIDAS, and are commonly used in regulated industries like life sciences, finance, and government.