Product Group
This is an information field is on the feed® product header. It is similar to "Supplier" and "Product Owner", and is often used to categorize products based on product groups/main groups in the ERP system.
Of course, it is completely optional how one wants to use this in feed®.
WooCommerce Module
If one has the feed® WooCommerce module installed, this field has some additional functionality associated with it, as one can set up different selection variables for base / variant products based on which product group the base product belongs to. If there is a need for different variables to select variants for different types of base products, one must use the product group to differentiate these bases.