In a ETL system a datastore is a data structure that can be used as a source or a target in a mapping. It can be:
a table stored in a relational database
an file (delimited, or fixed length)
a node from a XML file
Regardless of the underlying technology, all data sources appear in ETL+ in the ETL Source panel in the form of data stores/sources that can be manipulated and integrated in the same way.
Related Pages and Concepts
The Source Object and Target Object panels of the ETL+ Extract, Transform and Load (ETL) Page
(Target) data warehouses