A stock keeping unit (SKU) is a unique identifier assigned to a specific product or item in a company's inventory. It is used to track inventory levels, sales, and other relevant information related to the item. SKUs typically include a combination of letters, numbers, or symbols that help identify the product's attributes such as size, color, style, or manufacturer. By using SKUs, companies can improve their inventory management, reduce stockouts, and improve their ability to analyze sales data.