A database transaction is a sequence of operations performed as a single logical unit of work. It ensures that either all operations are completed successfully or none at all, maintaining the integrity of the database. This concept is crucial in scenarios where multiple users or processes access the database simultaneously, preventing data inconsistencies. Transactions typically follow the ACID properties: Atomicity, Consistency, Isolation, and Durability. These properties guarantee that transactions are processed reliably. For example, if a transaction involves transferring money between two accounts, it must ensure that the amount is deducted from one account and added to another, or neither operation occurs.