# External ID > The customer's own product identifier stored with a PhotoRobot item, for syncing status back. Also known as: external_id. Category: E-commerce and workflow. An external ID is the identifier of a record in another system, stored next to the local ID so both systems can refer to the same object. It lets two systems refer to the same product. ## How PhotoRobot uses it A PhotoRobot item can carry the ERP product ID. When the item is published, a [webhook](https://www.photorobot.com/glossary/webhook) handler looks it up and sends the status back to the ERP, the [status round-trip](https://www.photorobot.com/glossary/status-round-trip). Covered in module [I03](https://www.photorobot.com/academy/curriculum#i03-shooting-list-sku). ## Related terms - [Status round-trip](https://www.photorobot.com/glossary/status-round-trip): Sending an item's status from PhotoRobot back to the upstream ERP through a webhook. - [Mapping table](https://www.photorobot.com/glossary/mapping-table): An integrator's table linking canonical SKUs to PhotoRobot item IDs and external IDs. - [SKU (stock keeping unit)](https://www.photorobot.com/glossary/sku): A retailer's internal code for one distinct product variant. - [ERP (enterprise resource planning)](https://www.photorobot.com/glossary/erp): Business software that manages core processes such as inventory, orders and finance.