This counts properly-aligned frames that were discarded because of a CRC, or checksum, error. Because the frame is still octet-aligned, a rising CRC error count, distinct from the alignment-error counter, tends to point at signal integrity issues on the cable itself, such as electrical noise, a marginal connector, or a too-long or damaged cable run, rather than a timing or framing problem. A cable run near a source of electrical interference, like heavy machinery or power conduits, showing a rising CRC error count here while alignment errors stay low would point specifically at cable shielding or routing as the likely fix.