SKU (Stock Keeping Unit)
Definition
Your internal code for each distinct product variant you sell, such as each size and color, used to track inventory, sales and cost.
Want a deeper explanation?
SKUs are the unit that inventory, costs and margins should be measured at. A clear, consistent SKU structure is what makes product-level profit reporting possible.
Each channel may use its own ID, like ASIN or UPC, that maps back to your SKU. Watch for: the same product under different SKUs in different systems, which breaks inventory counts and costing.
Example
A t-shirt in 3 colors and 5 sizes is 15 SKUs, like TS-BLK-M for a black medium.