A DataSet is a cache of records retrieved from a data source. It works like a virtual data store: A dataset includes one or more tables based on the tables in the actual database, and it can include information about the relationships between those tables and constraints on what data the tables can contain.
The DataSet is a memory-resident representation of data that provides a consistent relational programming model regardless of the data source. The DataSet represents a complete set of data, including related tables, constraints, and relationships among the tables.
The DataSet object is central to supporting disconnected, distributed data scenarios with ADO.NET. The DataSet class is explicitly designed for data access independent of any data source. As a result it can be used with multiple and differing data sources, used with XML data, or used to manage data local to the application. The DataSet contains a collection of one or more DataTable objects made up of rows and columns of data, as well as primary key, foreign key, constraint, and relation information about the data in the DataTable objects.