What is ClickBank tracking ID?
Tracking ID is alphanumeric identifier which helps you tracking your traffic. For example ClickBank Tracking ID can help you determining which affiliate campaign works better. When you use the same ClickBank feed on two different websites and want to know which one brings more conversions, you can use different tracking IDs for these websites. So you use "website1" and "website2" as tracking IDs in your affiliate feed.
Then in your ClickBank account you will see which tracking ID brings more results.