trans·ac·tion / tranˈsakshən; -ˈzak-/ • n. an instance of buying or selling something; a business deal: in an ordinary commercial transaction a delivery date is essential. ∎  the action of conducting business. ∎  an exchange or interaction between people: intellectual transactions in the classroom. ∎  (transactions) published reports of proceedings at the meetings of a learned society. ∎  an input message to a computer system that must be dealt with as a single unit of work.DERIVATIVES: trans·ac·tion·al / -shənl/ adj.trans·ac·tion·al·ly / -shənl-ē/ adv.

transaction An input message to a system that, because of the nature of the real-world event or activity it reflects, requires to be regarded as a single unit of work and must either be processed completely or rejected. Where the processing of a transaction involves several changes to be made to a database, and for some reason the activity is interrupted and not completed, then any changes made to that point must be reversed (backed out) and a DBMS must provide facilities to ensure this happens. When the processing of a transaction has been completed satisfactorily the changes to the database are committed – made permanent.