FCS (Frame Check Sequence) and Alignment Errors: both are the result of collisions at half-duplex, duplex mismatch, bad hardware (NIC, cable, or port), or connected device generating frames with bad FCS, but have different meanings:
FCS error count is the number of frames that were transmitted/received with a bad checksum (CRC value) in the Ethernet frame. These frames are dropped and not propagated onto other ports.
Alignment errors are a count of the number of frames received that don't end with an even number of octets and have a bad CRC.
