A transaction log is a record that keeps track of all changes made to a database. It captures details such as the time of the transaction, the type of operation (like insert, update, or delete), and the data affected. This log is essential for maintaining data integrity and helps in recovering data in case of a failure. In many database management systems, the transaction log is used to ensure that all operations are completed successfully. If a system crashes, the log can be used to restore the database to its last consistent state, minimizing data loss and ensuring reliability in applications that rely on the database, such as banking systems or e-commerce platforms.