A web mashup is a web site that takes difference sources of information or functionality from one or more websites and present it in a different, unique way. A good mashup is where the most important information to you is cut out from 1 or many site and all brought together in one simple layout, without all the in between info you actually want.
Mashups i like!
Twitter Vision is a interesting example of a web mashup. It combines Google maps with live Twitter feeds to show where people are posting there tweets around the world. I really liked it because it is really well done, very unique mashup, and it was really simple, fun to just look at.
Flickr Sudoku is another interesting one, it’s the game Sudoku, but the numbers used in the game are Flickr search images.