This counts BTUs discarded because the specific circuit's forward bit, a per-circuit flag controlling whether traffic on it should be forwarded, was set off. A rising count here points to circuits that are provisioned but administratively blocked from forwarding, so an admin seeing this climb should check whether a PVC was intentionally disabled, such as during a customer suspension, versus accidentally left in a blocked state after a configuration change. For example, after suspending a customer's PVC by clearing its forward bit, an admin expects to see cardInForwardBitBtus start counting the still-arriving but now-blocked traffic for that circuit.