Is it a macro? A sharepoint customisation? A mashup?
What is important, in my mind, is that the user is shielded from the complexity (or lack of it) in the process and the application can just stay out of their way so they can do their job and keep using the tools they are familiar with, whether that is browser based (I would recommend SharePoint) or rich client (Word, Excel Powerpoint...).
Technically, I think this conceptual architecture explains it well:
From Office Business Applications: Pricing Exception Management Solution
OBAs are not just an Office Client thing, they are not the new flavour of macros (but they help us achieve things that we have tried to bend VBA to do for some time). It is all about linking in your backend line of business systems, to your organisations "squishy logic" that performs the bulk of the work (that means you, human!).
Many Office Applications are no-code solutions - All that needs to be done is to configure say, Word to talk to a SharePoint document library, define some metadata and create a workflow via a wizard in SharePoint Designer (or one of the out of the box SharePoint ones).
Or, it could be as complicated as writing .NET/Java code to generate a document on the server side, pulling fields from a number of databases and web services, Biztalk or the like.