Non-repudiation is the property of an information recording system to preserve the identity of the 
originator of a communication. (Or something like that.) If a system supports non-repudiation, a 
person can't claim that they didn't perform the communication (in the absence of a security 
breach). 

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Non-repudiation requires a contract between the parties that a particular non-reversible transaction has taken place and some sort of signature that validates that contract. More elaborate schemes include trusted third-party witnesses to confirm that the parties were physically present to sign the contract.

Computer equivalents follow the same reasoning.

Trading banks have a particular interest in such activities since they will trade for customers by proxy. For example, I could ask a trader to 'buy 1 million MicroSoft shares', then repudiate the deal if the share-price happened to drop. A non-repudiation safeguard avoids this sort of fraud, it also prevents the bank from claiming I had entered an order when I had not.

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Perhaps CategorySecurity or AuthenticationPattern