It means that not all IO operations complete in the same order as they were submitted.
Or if talking about UDP it's a property of the protocol that packets may arrive out of order (or not arrive at all).
I don't know if that is a reasonable explanation to OP's question though. Those are things that happen before
the IOCP message gets queued, so I doubt that is what that line would have been talking about. The IO completion port does not
have anything queued on it until an IO operation completes
, and then it gets queued. So unless that sentence was just a very poor choice of words, it can't be talking about the fact that the IO's don't complete in order, because they are not queued on the port, only their completion is
. Hence the name "IO completion port" :)
OP: Where'd that line come from, BTW?