Transaction

A transaction (also referred to as an online transaction) is "[a]n electronic communication among two or more parties (e.g., business, negotiations, activities, etc.) of a discrete unit of work brought to the mutually agreed conclusion or settlement. The parties have an obligation to play their parts during the transactions and honor their commitments after the transaction."

Source
The White House, (Draft) National Strategy for Trusted Identities in Cyberspace: Creating Options for Enhanced Online Security and Privacy 33 (June 25, 2010).