Piggyback Ack Timeouts is the number of times that a piggyback acknowledgment could not be sent because there was no outgoing ...

Piggyback Ack Timeouts is the number of times that a piggyback acknowledgment could not be sent because there was no outgoing packet to the remote on which to piggyback.  A piggyback ack is an acknowledgment to a received packet that is sent along in an outgoing data packet to the remote computer.  If no outgoing packet is sent within the timeout period, then an ack packet is sent and this counter is incremented.