Here is what I got back from HP, when I asked the same question.
Discards are specified as " ... Total number of Rx and Tx discards on the interface. Rx frames discarded are generally due to protocol errors. On rare occasions, a frame is received without any hardware errors, but a filtering rule set for the MAC address discards the frame due to a mismatch. Discarded Tx frames can be timeout frame discards (port is offline or not up), or timeout frames that are not sent back to the supervisor (class F/2 frames). If the Discards field is not empty, it is probably due to timeout frames.
