Count of CRC errors. CRC is an error detection code used to verify packet transmission between the sender and receiving end. A CRC error indicates that part of the data packet is corrupt and requires retransmission. – see Cyclic Redundancy Check (CRC) for a more in depth explanation.
Many CRC errors in a short period of time will show a noticeable reduction in throughput speed. This can be an early indication that there is too much noise on the line and in extreme situations can lead to loss of sync (disconnection with the exchange).