1. General: Agreement, contract, exchange, understanding, or transfer of cash or property that occurs between two or more parties and establishes a legal obligation. Also called booking or reservation.
2. Accounting: Event that effects a change in the asset, liability, or net worth account. Transactions are recorded first in journal and then posted to a ledger.
3. Banking: Activity affecting a bank account and performed by the account holder or at his or her request.
4. Commerce: Exchange of goods or services between a buyer and a seller. Every transaction has three components: (1) transfer of good/service and money, (2) transfer of title which may or may not be accompanied by a transfer of possession, and (3) transfer of exchange rights.
5. Computing: Event or process (such as an input message) initiated or invoked by a user or computer program, regarded as a single unit of work and requiring a record to be generated for processing in a database. In a secure transaction (see ACID qualities) such events are regarded as a single unit of work and must either be processed in their totality or rejected as a failed transaction.