The term mash-up refers to a new breed of Web-based applications created by hackers and programmers (typically on a volunteer basis) to mix at least two different services from disparate, and even competing, Web sites. A mash-up, for example, could overlay traffic data from one source on the Internet over maps from Yahoo, Microsoft, Google or any content provider. The term mash-up comes from the hip-hop music practice of mixing two or more songs.
This capability to mix and match data and applications from multiple sources into one dynamic entity is considered by many to represent the promise of the Web service standard (also referred to as on-demand computing).
Yahoo Maps Mash-Ups Begin Rolling Out Since Yahoo released an API for Yahoo Maps, developers have started releasing "mash-ups" that overlay various types of info on top of Yahoo Maps. Here's a list of a few of them.