A SKU is a business's own code for one specific sellable item — one product in one size, colour or pack — used to track its stock and sales.
Unlike a barcode such as an EAN or UPC, which is set by the manufacturer and read by scanners, a SKU is chosen by you and designed to be read by people. One item usually has both.
EXAMPLE
TSH-CREW-BLU-L for a blue crew-neck t-shirt in large.