A derived table is constructed by means of evaluating a table expression over the columns and values of its underlying table set. The semantics of derived tables are identical to those of views. In fact, a view is nothing more than a named derived table.
Derived tables allow you to specify a spool file composed of selected data from the underlying table set supporting the table expression in the FROM list of a query.
See SQL Data Manipulation Language, B035-1146 for complete documentation of derived tables.