iLok is a separate software that manages authorizations. Having an iLok USB allows you to carry your software licenses on a physical drive between a studio, your home and any other location you may be using iZotope software.
iLok is an optional authorization method with all iZotope software, Cloud and Computer license locations aren't currently supported.
Exponential Audio Products
Exponential Audio products all require iLok authorization to work but do not require an iLok USB. You can manage your iLok Authorizations via the iLok License Manager. To read more about authorizing Exponential Audio products, on the Exponential Audio authorization article.
You can get more information from the iLok homepage.