Inventory is the module that tells the truth about your shelves. It holds your warehouses, the stock in them, and the complete history of how every quantity came to be what it is: what was received, what was delivered, what was moved, what was counted, and what was corrected — each change written down as a movement with its document attached.
One law runs through the whole chapter, and it is worth meeting now: stock is never edited. Nobody types a new balance into a product and makes it so. Quantities change only when a document posts — a goods receipt brings stock in, a waybill takes it out, an adjustment corrects it, a transfer moves it — and every one of those changes stays on the record forever. If the shelf and the screen ever disagree, you do not fix the screen; you count the shelf and post the correction, with the reason attached. That is what makes the numbers worth trusting.
Used well, Inventory answers: What do we hold, and where? What is it worth? What is already promised to customers, and what is still coming in? What is about to run out, go stale, or pass its expiry date? And the question behind them all: can the warehouse and the books be made to agree — and proved to agree?