Once apon a time ... the definition of an application was easy - firms built accounts payable, general ledger, purchasing, order entry, and other applications to meet the automation needs of the business. The applications were written as monolithic collections of functionality that were dedicated to accomplishing key business functions and had relatively clear boundaries.

However, over the years, technology shifts have resulted in "applications" that don't fit the earlier simplistic definitions. DLLs, Services / SOA, ASPs and Software-as-a-Service (SaaS) all bent the definition of an "application" from its previous form. Looking forward, Cloud computing promises to alter the definition once again.