I first heard the word mashup at the MIX06 conference. Mashup (web application hybrid) as trend was mentioned at several sessions. These mashups use and combine webservices to create new applications. The programmableweb has a nice overview of some of these combinations in a matrix.
According to Wikipedia a mashup is also a musical genre. This genre uses parts of other songs to create new songs.
So basically combining stuff is not really new and if you look around you see it happening over and over again. Another good sample -and a very succesfull one- is the Senseo created by Philips and Douwe Egberts. But Nike and Apple take it to the next level.
