A Pack is when you have a listing that carries a higher quantity of a single product, while there is another listing that sells the same product but with a quantity of just 1.
Let's take an example you have an Amazon listing that sells a pack consisting of 3 phone charges. Then, you have a separate listing that carries just one phone charger.
To handle it in Planyard, you would create one product called "Phone Charge". Then you would map both listings to this one product. The single would be mapped with a quantity of 1, and the pack would be mapped with a qty of 3.
Please note, that in Planyard, every SKU needs to be mapped to a product. A single item would be mapped with a quantity of 1, and a pack is to be mapped with a higher quantity respectively.
Mapping is done best in Inventory>SKUs>Show Sidebar per below: