A mash-up is a general term that is commonly used to describe the merging of functionality and content from multiple sources. It is typically applied to describe the merging of web applications where the sources might often use a different technology to provide the service or application but as part of the distinction for a web application mash-up; the common feature that provides connectivity is the Internet.
The connections between the various sources might require different levels and complexities of integration depending on whether the associated information or content is to be simply viewed or whether it is also to be amended, and therefore, whether data is to be distributed across the various systems. When mash-ups first started appearing on the Web, they were quite simply created to enable the viewing of content from another web source within an Internet browser and did not transfer any data or functionality between the source systems.