Dear Mashup fans!
Well, maybe you're attracted by the hip-hop music Mashup and you think it's related to it! Nah! here is a simple definition from Wikipedia for Mashup:
"In technology, a mashup is a web application that combines data from more than one source into a single integrated tool; an example is the use of cartographic data from Google Maps to add location information to real-estate data, thereby creating a new and distinct web service that was not originally provided by either source."
Best site to start with Mashups is the Microsoft Popfly website (I was luckly to get a private invitation from Microsoft Popfly team to try it out in it's early alpha phase with the old domain popfly.ms), this site contains a very cool tools and a free storage for your mashup projects with tons of applications you can use to create a mashup. You can add news feeds, maps, Windows Live Spaces, Weather..... and even facebook!
Get started now: www.popfly.com
Best of luck mashers! ;)