A Multipack SKU is a SKU that has multiple units of an underlying "Single" product. An example is a pack of 5 bars of soap. That pack of 5 likely uses the same UPC as the single unit SKU for that bar of soap, so we need a way to tell each channel that the multipack SKU is actually 5 units, not 1 unit.

The Multipack Quantity field is to be used when a Kit SKU cannot be created because you do not sell the underlying single unit. In the GENERAL INFO section of the edit view for a given SKU.

So, using the example above, you would enter 5 in the Multipack Quantity field if and only if you don't have the underlying single product SKU in your catalog which is needed to create a Kit SKU in Zentail.