An ASN (Advanced Shipping Notice) is an electronic document sent by a supplier or shipper to notify a warehouse of an incoming delivery before it arrives. It typically includes shipment details like SKU numbers, quantities, carton or pallet breakdown, expected arrival time, and carrier information. 

ASNs allow receiving teams to prepare space, staff, and equipment in advance, and help speed up check-in by enabling pre-validation of the shipment. For example, if a supplier sends an ASN listing 10 pallets of mixed SKUs, the WMS can preload expected stock data and trigger automated putaway once the shipment is scanned.