Write-Ahead Logging (WAL) is a technique used in databases to ensure data integrity. It works by recording changes to a log before they are applied to the actual database. This way, if a system crash occurs, the database can recover by replaying the log entries, ensuring no data is lost. WAL is particularly useful in systems that require high reliability, such as transactional databases. By writing changes to the log first, it allows for quick recovery and minimizes the risk of corruption. This method is a fundamental part of many modern database management systems, enhancing their robustness and performance.