well BI is I believe business intelligence, which is sort of like military intelligence, the set of practices and tools that have evolved around the need to present data to business people in such a way that they can make sensible decisions regarding their business.

on edit: So a dashboard is just one of those things were you see all the things you can do or interact with assembled together and from which you can navigate into any particular tool or view of data. Probably there would be meaningful data views on top. Like Number of Purchases versus people who started a purchase. And you could then drill down into the data that this chart represented to see how long purchases took, repeat customers, when people leave process or purchase etc. etc.

The dashboard is the entry point for how you will navigate your business data.