A web mashup is a web application that takes information from one or more sources and presents it in a new way or with a unique layout.
It is actually not quite so difficult to understand as the technical definition might make you believe. The key driving power of the Internet is information, and a mashup is an application that takes that information and shows it to you in a unique way.
For example, the Nintendo Wii has been difficult to find in stores. A web mashup might help by taking the data from various stores like EB Games and other websites like Ebay and combine this information with Google maps to present you with an easy-to-use interface for finding a Wii in your area. To see this in action, you can visit FindNearBy.
How is a Web Mashup Built?
The web is continually growing more open and more social. Because of this, many websites have opened up programming interfaces (API's) that allow developers to get at their core information.
A prime example of this is Google Maps, which is a very popular interface to use in mashups. Google allows developers to access their maps through API's. The developer can then combine these maps with another stream of data to create something new and unique.
Must a Web Mashup Have Contain Data From Multiple Sources?
The name "mashup" is derived from the idea of combining data from two or more sources and displaying it with a unique look. However, newer mashups sometimes only use a single source of information. A good example of this is TwitterSpy, which only pulls data from Twitter.