Tracked stock belongs to one item and one location. The item can be a simple product, a product variant, or an inventory group shared by several products or variants.
On-hand and available stock
On-hand quantity is the physical count recorded at the location. Reservations do not change that physical count. Available stock is on-hand minus reserved stock.
Changing stock
Use an adjustment when stock was received, returned, damaged, lost, recounted, or corrected. An adjustment adds or subtracts a delta safely under concurrent work. Set quantity replaces the count with an absolute physical count and is best reserved for reconciliation after a count.
Every successful change writes an immutable movement with the item, location, quantity change, resulting quantity, reason, actor, and any order or transfer reference. Store Admin, the mobile app, CSV jobs, Store API apps, transfers, and order fulfillment all use the same ledger.
Low-stock rules
A location-level threshold is low when available stock is at or below that threshold. Inventory groups can also have an overall threshold across their locations. A threshold is an alerting rule; it does not prevent sales.