All of your Inventory Stats can be found in the "Inventory" section of your store's dashboard. On the right hand side you will see 3 columns.
The Sold column displays the quantity of items your customers have paid for. Whether that's an instant purchase using money they have available, or an eCheck that has or hasn't cleared yet. This number also includes any free items you've given away.
The Held column displays the quantity of items your customers are currently at PayPal paying for. This number is removed from the "remaining" number while they're held. If your customer abandons the order, the inventory hold is released and the items will return to the "remaining" column. If your customer completes their order, the inventory hold is released and the items will appear in the "sold" column.
The Remaining column displays the quantity of items still available to your customers.
Tips: If you click the product row it will display the "Sold", "Held", and "Remaining", across all variations of that product.