Datawarehouse and Datamarts

Data Warehouse
A data warehouse is a centralized repository containing comprehensive detailed and summary data that provides a complete view of customers, suppliers, business processes, and transactions, from a historical perspective with little volatility.
Advantages

Improve data qualityMinimize inconsistent reportsCapture and provide access to business metadataProvide capability for data sharingIntegrate data from multiple sourcesMerge historical and current data appropriatelyImprove the speed and performance of all reporting needs

Data Mart
Contains a subset of the data stored in the data warehouse that is of interest to a specific business community, department, or set of users (for example: marketing promotions, finance, or account collections)
In a well structured BI system, the data warehouse serves as a single source for multiple data marts