The Free On-line Dictionary of Computing (30 December 2018):

database transaction

    A set of related changes applied to a database.  The
   term typically implies that either all of the changes should be
   applied or, in the event of an error, none of them, i.e. the
   transaction should be atomic.  Atomicity is one of the ACID
   properties a transaction can have, another is isolation -
   preventing interference between processes trying to access the
   database cocurrently.  This is usually achieved by some form of
   locking - where one process takes exclusive control of a
   database table or row for the duration of the transaction,
   preventing other processes from accessing the locked data.

   The canonical example of a transaction is transferring money
   between two bank accounts by subtracting it from one and adding it
   to the other.

   Some relational database management systems require the user to
   explicitly start a transaction and then either commit it (if all
   the individual steps are successful) or roll it back (if there are
   any errors).

   (2013-06-03)