Previously I talked about IBM Enterprise Mashup. So what is a Matchup?
I talk about it (where else?) on my wiki at Mashup.
My take is that a mashup app is basically a composite app, like a portal. I've coined a new term, mashlet, which is like a portlet but for mashup content sources. I contend that a mashlet is what we've been calling a service. Nevertheless, let's see if the term catches on!