Metrics in online advertising

There are quite a few metrics in online advertising. Some of them are easy to understand. Some are not.

Here you'll find definitions of both the easy ones and the not so easy ones.


What is really the difference between CPM and eCPM? And is really CPM a metric or a payment model in online advertising?
Buying methods explained
Definition of CPM
Definition of eCPM

Calculation methods

And how do we calculate these metrics?
How to calculate CPM
How to calculate eCPM