a.k.a. mash-up, mash-up sites, mashing, Web mash-ups, Web mapping
A mashup is a Web page or application that integrates complementary elements from two or more sources. Mashups are often created by using a development approach called Ajax. Here's an example of a few mashup sites:
Diggdot: a mashup of Digg, Slashdot and Del.icio.us that integrates and filters content
Flash Earth: a zoomable mash-up of Google Maps and Microsoft's Virtual Earth
Hiking Outpost: a mashup of Amazon and online hiking information resources
HousingMaps: a mashup of Google Maps and Craigslist rental ads that displays geographical information for rental properties
Panoramio: a mashup of Google Maps and geopositioned photographs of locations.
Like blogs, vlogs and tagging, mashups are part of an ongoing shift towards more a more interactive and participatory Web 2.0 with more user-generated content and services. Mash-ups illustrate the Internet's underlying philosophy: Open standards allow and promote unexpected forms of innovation.
As reported in the Washington Post, here is a look at the significance of mashups: The proliferation of Web 2.0 was made possible through the integration of various programming languages, referred to as mashups, which often are created by users who have no association with either site used in the mashup. Sites such as Facebook and Google offer application programming interface (API) code that developers can use to create new applications based on the code of the original site. An open site with APIs allows for the creation of mashups and, in turn, further spreads the reach of the original sites. While companies may consider opening the back-end of their sites through APIs, others are taking an additional step by offering Software as a Service (SaaS), which is software that lives online vs. downloads and applications that are housed on a user's desktop. This decreases the need for downloads and space on a computer, as it instead lives within a user's browser, making it accessible to the user from anywhere and from any computer.
The term "mashup" originated in the music industry. According to Aaron Boodman in BusinessWeek, "The Web was originally designed to be mashed up. The technology is finally growing up and making it possible."