A "Non-Repeatable Read" occurs in database transactions when a transaction reads the same data multiple times and gets different results. This inconsistency happens because another transaction modifies the data between the reads. For example, if Transaction A reads a value, and then Transaction B updates that value before Transaction A reads it again, the results will differ. This phenomenon is a concern in database management systems, particularly in environments where multiple transactions occur simultaneously. To prevent non-repeatable reads, systems can implement isolation levels, such as Serializable or Repeatable Read, which help maintain data consistency during transactions.