Inventory SKUs describe a collection of Inventory Items that share the same Name, Amount/Units, and might share the same Barcode/UPC. Values stored on a SKU are shared with all of the Inventory Items that belong to this SKU. You can create your own Custom Fields to store values that aren't unique for each physical Inventory Item in Kn{owl}edge. SKUs are assigned to Inventory Categories.
Here's where they fit in the structure (Inventory SKU are in bold)
As you can see, Inventory SKU are assigned to Inventory Categories and Inventory Items are assigned to an Inventory SKU.
Here's another example of how a video game store might organize their inventory: (Inventory SKUs are in bold)
In the above example the video game store choose to have a parent Inventory Category of "Console Games" and then subdivide those into console games for various gaming systems. The Inventory SKU "Uncharted: The Lost Legacy" is a Playstation 4 game and so they assigned it to the Inventory Category "Playstation 4 Games". Each Inventory SKU has a unique barcode, either from the UPC barcode already on the product or auto generated from Kn{owl}edge. Each Inventory Item that is assigned to an Inventory SKU represents the physical item on the shelf.
The following are fields that you might see on an Inventory SKU edit page. Some of the following fields are optional so they might not display depending on your account configuration.
The Usage Type of a SKU describes how Inventory Items of this SKU are used within Kn{owl}edge.
SKUs that are discontinued will still retain their historical information but won't show up in SKU search fields. Discontinuing old SKUs that you no longer carry helps keep your list of SKUs tidy. It's recommended that you mark SKUs as discontinued when you no longer plan to carry the SKU anymore. You can always edit the SKU later to bring it back into the SKU search results.