In the warehouse context, reserving stock means indicating that a specific part of the inventory is already committed to an order or promise, so it cannot be used by other orders.
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At location A3, we don't want any outbound orders because the stock there is reserved.
Set the Block Outbound column to Yes.
At location B1, we don't want any inbound orders because there is no available space.
Set the Block Inbound column to Yes.