Data marts are for the most part intended for a solitary branch of business. They are designed for the individual departments. For example, I used to work for a health insurance provider company which had different departments in it like Finance, Reporting, Sales and so forth.

We had a data warehouse that was holding the information pertaining to all these departments and then we have few data marts built on top of this data warehouse. These DataMart were specific to each department. In simple words, you can say that a DataMart is a subset of a data warehouse.