A database transaction is a sequence of multiple operations performed on a database as a single logical unit of work, taking place wholly or not at all, ensuring data consistency and reliability in the event of system failures or concurrent requests. Transactions are needed to ensure that the outcome is reliable and consistent, isolating requests from each other to avoid conflicts, and providing atomicity, consistency, isolation, and durability properties to guarantee that a transaction is processed reliably. These properties, commonly abbreviated as ACID, ensure that a database transaction is processed reliably, with atomicity ensuring all or nothing, consistency maintaining data integrity, isolation keeping transactions independent without affecting others, and durability guaranteeing a successful transaction commit will survive permanently.