A data mart is a narrowly focused database—in some ways a smaller version of a data warehouse, though lacking the same scope of resources and functionality that are the hallmark of a data warehouse. Multiple data marts, called dependent data marts, can be contained within a single data warehouse—some data warehouses are made up of many data marts.
Data marts are used when only a subset of data is needed or desired for computation and analysis. Data marts might be created around a single subject, for individual business departments (marketing, sales, etc.), or by those to whom a complete data warehouse is not available.
http://en.wikipedia.org/wiki/Data_mart http://www.rapid-business-intelligence-success.com/data-mart.html http://www.webopedia.com/TERM/D/data_mart.html