FOB is an acronym that stands for “Free On Board”, a term used to indicate the point at which responsibility for the goods and the costs associated with their delivery change hands. In other words, for FOB orders, the delivery type, its charges, and label generation are all handled by the marketplace. Here at VTEX, it can be used as a delivery method for the following marketplaces: Magalu, Mercado Livre via Mercado Full Envios, and B2W via B2W Entrega.
We have documentation in our Help Center that covers this topic:
These orders can be identified in the OMS under the Delivery Type section, which typically lists the carrier/shipping strategy selected, but in this scenario will show vtex:fob_XXX, where XXX corresponds to the ID of the Dock chosen for the fulfillment process.
Or through the Get order API, in the selectedSla, deliveryCompany, or courierName fields within the logisticsInfo array:
If you still have any questions about this topic, feel free to ask right here! 
Karina Mota
Field Software Engineer | VTEX