Microsoft SQL Server includes a popular command-prompt utility named bcp for moving data from one table to another, whether on a single server or between servers. The SqlBulkCopy class lets you write managed code solutions that provide similar functionality. There are other ways to load data into a SQL Server table (INSERT statements, for example), but SqlBulkCopy offers a significant performance advantage over them.
The SqlBulkCopy class can be used to write data only to SQL Server tables. However, the data source is not limited to SQL Server; any data source can be used, as long as the data can be loaded to a DataTable instance or read with a IDataReader instance.