Reserved Inventory in Amazon means a few things. Reserved Inventory can be broken down into 3 categories.
Customer orders - These are units that have been sold but not yet shipped to your customers. That means these units are already sold and are not available to be sold again.
FC transfer - These units are being transferred from one fulfillment center to another to place your inventory closer to customers. Units in FC Transfer status are available for customers to buy but customers might be shown a future ship date (back ordered) if you don't have any other units available for immediate fulfillment.
FC processing - These units are at the fulfillment center and going through additional processing (product check in, verification of item dimensions and weight, or pending investigations, etc.). While these units are usually not available for sale currently, they will be made available for you to sell in the future (pending successful processing).
To see the status of your reserved inventory, go to your Manage FBA Inventory tab in Seller Central and hover over the reserved amount for each product (image below).
Note: When inventory is being processed for transfer to another fulfillment center, those units might show up under both "FC Transfer" and "FC Processing" for a short amount of time. Units in "FC transfer" are available for sale, but cannot be eligible for Prime delivery until they are transferred to destination FCs.
