查了一些文件(ECMA 267)，看來應是這樣了吧

PI Errors:
A row of an ECC Block that has at least 1 byte in error constitutes a PI error

PI Failures(PI-uncorrectable): (no more than 5)
If a row of an ECC Block more than 5 erroneous bytes, the row is said to be “PI-uncorrectable” (Called PO in K-Probe)

PO Failures:
In any ECC Block the number of PI-uncorrectable rows should not exceed 4.
PS:
Actually the PO errors that K-Probe reports is the Parity Inner uncorrectable errors, meaning errors left after PI correction