datamart is nothing but a database. it can be stored data
about the particular orginazation.

A data mart is a particular subject oriented block of data 
in the datawarehouse in the business line like production, 
sales, marketing etc. they are two kinds of datamarts are 
there one is independent & Dependent datamarts.

sub set of datawarehouse is called data mart.

A data mart is a subset of data warehouse that is designed 
for a particular line of business such as sales, marketing, 
finance, etc. 
Data mart is of two types:
1) Dependent data mart, in which data can be derived from 
an enterprise-wide data warehouse. 
2) Independent data mart, in which data can be collected 
directly from sources.

In the industry when a organisation goes for a enterprise 
wide Datawarehouse the cost involved in setting up . its 
maintenance and other overheads are also associated with 
it. So due to budget and time constraints some 
organisations initially set up a Data Mart to facililtate 
there immediate needs . These Data Marts are generally set 
up at department levels and in a future date if utility 
arises then datamarts across the organisation can be 
integrated and a full fledged data warehouse can be formed. 
In a way Data Mart is a subset of Data Warehouse.

Data Marts is used on a business division/department level. 
A data mart only contains the required subject specific 
data for local analysis. 
   A database, or collection of databases, designed to help 
managers make strategic decisions about their business. 
data marts are usually smaller and focus on a particular 
subject or department. Some data marts, called dependent 
data marts, are subsets of larger data warehouses. A data 
mart is a simpler form of a data warehouse focused on a 
single subject (or functional area) such as sales, finance, 
marketing, HR etc. Data Mart represents data from single 
business process.