Answer:

An Extended Initial Activation Key is a code that may be used to activate Foxhound Version 2 as an Extended Edition copy after

• installing a fresh copy of Version 2 without upgrading from an existing copy of Version 1.x, or

• upgrading an existing copy of the Version 1.x Evaluation Edition to Version 2.

In both cases the Foxhound Activation page will appear automatically when you start Foxhound, and entering an Extended Initial Activation Key will be one of the alternatives.

An Extended Initial Activation Key may also be used to change the Rental Edition to the Extended Edition; see the Renew or Upgrade Foxhound button on the About page.

You can purchase an Extended Initial Activation Key here:

See also...
What are the differences among the different editions of Foxhound: Rental, Basic and Extended?
What are the differences among all the activation keys?