It enables the use of one parameter for passing the unique click ID for all offers of this affiliate network.

Tracking token is a parameter used by our tracker for passing the value of a unique click ID. In this field, you should specify the name of this parameter provided by your affiliate network, in which it can receive the unique click ID of our tracker, and it is then be added to the offer link. 

For example: if your affiliate network is created on the Cake platform, you may use s2, s3, s4, s5 for Tracking token. If it is created on the HasOffers platform, then you may use aff_sub2, aff_sub3, aff_sub4, aff_sub5.
Also, there are affiliate networks created on custom platforms. And it is necessary to check this value from affiliate manager for each one of them.
​Please note: this field is useful only when the affiliate network has a standard format of an offer link, that is: http://offerurl.com?parameter1=value1&parameter2=value2...
If the format is different, then this field can't be used.