What is "transactions"

Tag referring to database transactions that is characterized by a sequence of operations in a database management system that are treated as a single, indivisible (atomic) block during a failure recovery and also provide isolation between concurrent accesses in the same mass of data. The SQL standard defines four transaction isolation levels (Read Uncommitted, Read Committed, Repeatable read, Serializable) in terms of three phenomena that must be avoided between simultaneous transactions. Unwanted phenomena are: Dirty read (dirty read) (Uncommitted), nonrepeatable read (read that cannot be repeated), phantom read (ghost read).