The thing they all have in common is "archiving" -- long-term storage and preservation of data that's inactive...
but may be needed in the future. However, the difference is in the types of data that are being archived. For example, structured data typically includes database records. Unstructured data includes documents, images and a wide range of other file types. Semistructured data often refers to email systems where unstructured email text and attachments are stored within structured databases. Some vendors try to do it all through a single unified product or separate products within a family (aka a "suite").
The point is that each archiving product has a different focus. File archiving products tend to work with unstructured data without regard for the originating application, offering powerful data movement, indexing/search and policy-based retention and deletion features. By comparison, email archiving focuses on archiving email packages, like Microsoft Exchange, but one tool may emphasize the role of content searching, while others may emphasize high availability and replication for disaster recovery. It's easy to see email archiving combined with other features. For databases, archiving is tightly integrated with specific applications, such as Microsoft Access, Oracle or SQL as well as third-party vendors.
Go back to the beginning of the File Archiving FAQ Guide.