In the admin panel, when you select a product and go into the variants information panel you might notice there are 3 different stock types. This article will be about Reserve stock
A products inventory goes into reserve whenever a cart changes into the "Placed State" or in the "Placed" column of the POS orders screen.
Reserve stock takes stock from your Units in stock inventory (total inventory) and places them in a state where it cannot be touched until the placed order is cancelled. This helps prevent customers from ordering over the stock limit.
For example, let's say a product has only 1 stock remaining but 3 customers place an order for the same product. Putting the product in reserve will serve the product on a first come first serve basis preventing a situation where 3 customers arrive, with their orders in hand, but only 1 product in stock.
Since reserve inventory pulls from the Units in stock it will affect any audits performed during this time. The audit will take from the "Units in Stock" since the stock in reserve is expected to go to a customer. If you are planning to do an audit its best to do so when there are no orders in the placed column.