Michael, Oracle 9 introduced the concept of system managed rollback
using an undo tablespace. The undo tablespace contains undo segments.
Prior to version 9 rollback tablespaces which contained manually
managed rollback segments performed this function.

You will need to look at the context of the material to tell if the
documentation is using the term undo in a generic sense that covers
both undo and rollback operations which are basically the same or is
talking directly about system managed undo and how Oracle manages it.

HTH -- Mark D Powell --