The term "mashup" has several meanings. It was originally used to describe songs that meshed two different styles of music into one song. For example, a classic rock song put to a well-known hip-hop beat may be considered a mashup. It is also used to describe videos that have been compiled using different clips from multiple sources. For example, a skateboarding movie created from several different skateboard videos found would be considered a video mashup.
A mashup also describes a Web application that combines multiple services into a single application. For example, a Web forum may contain a mashup that uses Google Maps to display what parts of the world the users are posting from. Yahoo offers a mashup called Yahoo! Pipes that aggregates RSS feeds into a single page that can be navigated using a graphical interface.
The primary purpose of most Web mashups is to consolidate information with an easy-to-use interface. Because the combinations of Web applications are limitless, so are the possibilities of mashups. Therefore, as mashups continue to evolve, don't be surprised to see them popping up on your favorite websites. After all, we can always use new tools that help make information easier to find!