The total number of TCP segments received in error, for example those with bad TCP checksums. A rise here specifically points to corruption happening in transit before the segment reaches this device's TCP stack, worth distinguishing from application-level connection failures since it implicates the physical or network path, a flaky link or buggy intermediate device, rather than anything the gateway's policy is doing. Example: tcpInErrs climbing only on connections traversing one particular WAN link, while other paths stay clean, points to a checksum-corrupting problem specific to that link's hardware.