COD shipping, or Cash on Delivery shipping, is an eCommerce payment and fulfillment model where customers pay for their order when it is delivered instead of paying online in advance. It helps sellers attract more buyers, especially in trust-sensitive markets, but it also brings challenges like higher RTO, delayed remittance, fake orders, and operational inefficiencies. A smart shipping system helps businesses manage COD better through tracking, NDR handling, reattempts, and faster remittance visibility.