What does non-repudiation in a signed e-mail mean?

A feature of a Digital Signature which allows the author ("signer") of a message to prove his identity. Non-repudiation allows you to prove later who participated in a transaction - a signer of a document of one end of a transmission cannot deny having sent the message nor can the recipient deny having received it. Simply stated, non-repudiation means that information cannot be disclaimed, similar to a witnessed handwritten signature on a paper document.