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

data mart

    A type of data warehouse designed primarily to
   address a specific function or department's needs, as opposed
   to a data warehouse which is traditionally meant to address
   the needs of the organisation from an enterprise perspective.
   In addition, a data mart often uses aggregation or
   summarisation of the data to enhance query performance.
   However, it is important to maintain the ability to access the
   underlying base data to enable drill-down analysis as
   necessary.

   (1998-04-24)