What is a Mash-Up?

Gordon Snyder and I have given a number of presentations on Web 2.0, Social Networking and the vast array of web-based tools that are starting to impact teaching and learning. One of these tools - mash-ups - is probably the most difficult to explain and the most difficult for people to grasp. I've always loved Gordon's explanation, comparing a mash-up to one of the ice cream creations at Cold Stone Creamery - where they take a bunch of diverse ingredients and mash them together right in front of you. Here's the Boston Cream Pie (French Vanilla Ice Cream, Yellow Cake, Fudge and Whipped Topping) hmmm:

Here's a 5-minute video with a slightly more technical explanation of mash-ups.