what for is column data type Business Data in Sharepoint Column Data Types?

I know that it lo开发者_如何学JAVAoks uo data from Business Data Catalog, but what kind of information/data can it be?

In a Business Data column (aka External Data) are the primary keys of the external data record stored. This column acts as a foreign key column that points to a certain record. When adding such a column to a list, one can specify which other fields of the entity should be displayed in the list.