A system of data and programs that address current system shortcomings. It may range in sophistication from a manually maintained word processing or spreadsheet document to a database with programs. It typically includes local data sources and either link to or copy of some SIS data.

Shadow system is a term used in Information Services for any application relied upon for business processes that is not under the jurisdiction of a centralized Information Systems department. That is, the Information Systems department did not create it, was not aware of it, and does not support it.