OK, so it's sort of a made up word. It comes from a model developed by Jakob Nielsen and Agency.com. I use it to do online Competitive Audits. One of six axes:
1. Accessiblity > SEO and SEM.
2. Immersibility > How easy is it for the user to immerse themselves in the experience? It's made up of heurisitics like wayfinding, status and visibility.
3. Content > Depth, breadth and recency.
4. Capability > What tools and widgets are there?
5. Community > Can the user talk to others, read reviews ask for expert opinion?
6. Commerce > If applicable, how elegant is the e-Commerce engine?