In Adzerk terminology, "Inventory" refers to information about WHERE the ad placement is appearing. It also lets you group together websites and domains for easier targeting. This is particularly useful if you manage a lot of sites (for instance, your native ad unit appears on 10s or even 100s of other websites).
Inventory also keeps tracks of ad sizes (pixel size), which is a required parameter in the Decision API request. The ad size makes sure we return an ad that will fit in the ad slot.
Everything lives under "Network" - or a single ID associated with your entire account.
Below are some illustrations of the taxonomy of Inventory.
This structure refers to most of our clients. The major differences compared to a multi-site publisher are (1) the use of only one channel and (2) the use of only three sites.
This structure is more applicable if you are a network or otherwise managing multiple websites with different themes and domains.