A business dashboard is a visual display of the most important information needed to achieve one or more goals. The information is arranged on one screen (or in a related set of screens) so it can be monitored at a glance.
This one’s really cool to look at, but it takes up lots of screen space and it could be using graphics that get its point across faster.
- Dashboard with Sparklines and Bullet Graphs
Here’s an example of a dashboard that can adapt itself easily to mobile access:
User Experience Design 
Dashboards, in my experience, can be more than one page. They key to their success is that they provide ready access to critical information in order to facilitate action. This can result in a long page but providing it is well designed it can still be very effective.
You are so right. There’s a lot more to a dashboard than just one screen can accommodate. Dashboard pages can be broken into many linked pages, like a website. A dashboard can be designed to allow the user to “drill down” or click on a subject and be taken to a screen with even more metrics.