What are Data Marts ?

Answer:

Data Warehousing is a process in which the data is stored and accessed from central location.
Data Marts are smaller section of Data Warehouses which help data warehouses to collect data.
For example your company has lot of branches which are spanned across the globe. Head-office of the company decides to collect data from all these branches for anticipating market. So to achieve this IT department can setup data mart in all branch offices and a central data warehouse where all data will finally reside.