An “inventory” or a “stock” is a list of items that are currently part of your warehouse, of your shop, of your household or just of your ownership.
We call these items “products” because most of our customers use the app for recording and tracking products in their warehouse or shop.
You can add and manage multiple inventories (resp. product lists). “Master data” is the part of data that is unique for all lists in the database. For example, master data contains the product ID, name, description, category, etc. Any modification of these data fields in an inventory will also take effect in all other lists.
As opposed to this, “Inventory data” is the part of data that can differ in each list (if you have multiple inventories), e.g. quantity, price, location, serial numbers, etc.