SKU
The unique code for one exact sellable item. Not 'the hoodie', but the black hoodie in medium. One SKU, one distinct sellable item.
See it
What it is
A SKU (stock keeping unit) names one exact sellable thing. Not 'the hoodie', but the black hoodie in medium. Every purchasable combination of options gets its own SKU, and that code is what inventory, orders, picking lists, and returns all point at. It is yours to invent, unlike a GTIN/UPC/EAN barcode, which is a global identifier issued by a registry.
Reach for a SKU scheme the moment a product has variants or you track stock in more than one place. Good schemes are short, uppercase, and readable at a glance: HOOD-BLK-M beats a random 12-digit number when someone is standing in a warehouse squinting at a label. One SKU does not mean one bin, either: the same SKU's units can sit in three warehouses, two retail stores, and a 3PL at once, counted per location.
Gotcha: never reuse a retired SKU. Old orders, old spreadsheets, and the 3PL's system all still reference it, and recycling the code quietly merges two different products in your history. Second trap: encoding meaning that changes (season, supplier, price tier) into the code, so the SKU starts lying the first time anything moves.
Ask AI for it
Add SKU-level tracking to this store: every purchasable combination of product options gets its own immutable SKU string in the format PRODUCT-COLOR-SIZE (uppercase, hyphenated, e.g. HOOD-BLK-M). Store the SKU on the variant, not the parent product, and key stock counts and order line items to it. Show the selected variant's SKU on the product page under the price in small uppercase monospace, muted gray, and update it live when the shopper changes size or color.