Definition of "economic moat"

I keep seeing the word “moat” lately in regard to investing, so I just looked up and found this definition. When I think of a moat, Apple comes to mind right away. I’ve been thinking about getting an Android phone recently, and then I realized that all of my friends and family use iPhones, and we use iMessage for free, and if I switch to Android, that goes away. Integrating an Android phone or tablet with iTunes also seems to be problematic, so it’s hard to get away from Apple. Facebook has a similar advantage, where it would be hard to get everyone to get up and move over to another social web service.