Inventory is a complete list of items that someone owns or has in stock. A store keeps an inventory of all the products on its shelves so it knows what needs to be reordered. A library maintains an inventory of every book it owns. When your teacher takes inventory of classroom supplies before the school year starts, they are counting markers, notebooks, and scissors to see what's available.

The word is used for keeping track of valuable things. Before computers, shopkeepers wrote inventory lists by hand in thick ledgers. Today, warehouses use barcode scanners to track inventory automatically, but the purpose remains the same: knowing exactly what you have.

As a verb, to inventory means to carefully count and record everything. If you're moving to a new house, you might inventory your belongings to make sure nothing gets lost. A restaurant inventories its food supplies to plan the next week's orders.

The word can also describe the items themselves. A bookstore with a large inventory has many books in stock. When something is out of stock, the store has none left to sell. Managing inventory well means having enough of what people want without wasting space on things that sit unused.